It is necessary to re-order the words of this stanza: Jórunn seemed to “the one coming with the gods” (Loki) (such that she) was not the door for the answer (the answer will not be obtained through her). Sad illness was for (helped to) the denial (Jórunn's), but both all less (very little) helped the speech.

Cleasby notes that the Icelandic uses jamt almost as an adverb in order to point at equality between two parts, this is why I put this word at the end of the sentence to show that unhealthy sadness and being shut to answering are the two sides of the same problem.

The destituted Goddess receives here a fourth name: Jórunn. Note it is built as Íðunn, suggesting a link between the beginning and the end of the story. The 'wave of the achievement' becomes the 'wave of the horse' (jór = horse), where the horse is a wild animal linked to sorcery, thus Jórunn can be understood as the wave of wilderness or of sorcery.

The nouns sút and sóttu both mean 'sickness, sadness' this is why I translate them by the equivalent 'saddening sickness' and 'sickening sadness'.

Note that jólnum komin (coming with the gods) points at Loki and sollin sútum (swollen with saddening sickness) points at Jórunn. Nevertheless, their nearness evokes that Loki can as well be affected by a saddening sickness.
The verb koma (past participle komin of the 2^nd verse) means to come, and hints at the necessity of coming for a specific goal. It fits perfectly someone in charge of a task.

Why is Loki the only one still able to observe Jórunn? We saw that Heimdall lost his marbles, and next stanza will tell us that Bragi turns into stone, thus Loki is the only one still able to work (ref. s.1, v. 1! Here is yet another example of the 'Odinic features' of Loki, hinted at in many texts making of Loki a kind of Óðinn's twin enemy).

        
16                
Fór frumkvöðull      He travelled, the leader         
fregnar brauta,        asker of ways,        
hirðir að Herjans      shepherd for Herjan        
horni Gjallar;            of the Gjallarhorn; [= Gjallarhorn's keeper for Óðinn]        
Nálar nefa                 Of Nál the nephew         
nam til fylgis,            took as follower         
greppur Grímnis      the poet of Grímnir         
grund varðveitti.      the field marked off.        

Herjan, the 'army leader', is yet another of Óðinn's names.
Heimdall is the keeper of the Gjallarhorn, the horn into which he will blow to call for the final battle, the Ragnarök.

Nál is Loki's mother, her 'nephew' (actually nefi also means 'parent') is Loki himself.
Grímnir, 'the hidden one', is again Óðinn; his poet is Bragi.
It is recalled here that Bragi and Loki travel with Heimdall. Óðinn seems to be said to be the owner of the Gjallarhorn.

This stanza says again known information, insisting on the fact that Heimdall is Gjallarhorn's keeper, and Loki Nál's son. The role of Bragi deserves an explanation.
Grund means a field, the ground (poetry uses it also for the Earth), and the flat bottom of a pan. The word varðveitti is made of varð-veitti. Varða is a stone showing a way. The verb veita (with the past form veitti) means to grant, to provide. Thus, varðveitti is something like 'granting a stone sign'. Within this context, it can mean either that Bragi shows the way to a field (as would be a cairn) or that he limits the field. The usual translation says that he “stood watch,” a very strange occupation for a poet. Inversely, the meaning of the words suggests that he stays transfixed in stone, now motionless like a road sign. This interpretation agrees with the fact that the reaminder of the poem never speaks of Bragi again. In particular, in stanza 20, Heimdall and Loki are asked a large number of questions, and none are asked to Bragi who should normally be in charge of telling the story. This suggests that Bragi stays with his ex-wife, transformed into a kind of stone pole.

Anyhow, he can keep watch or be transfixed, in both cases he is made useless.

17                        
Vingólf tóku        Vingólf they caught        They reached Vingólf        
Viðars þegnar,    of Viðar the warriors,    the warriors of Viðar,        
Fornjóts sefum   by Fornjót's sons            by Fornjót's sons         
fluttir báðir;        floated both;                    both carried as if by a stream;        
iðar ganga,           Inside they go,               Inside they go,        
æsi kveðja            the Aesir address,         they speak to the Aesir        
Yggjar þegar        of Yggr at once              at once, they join in        
við ölteiti.              towards beer joy.         the beer feast of Yggr.        

Vingólf means “pleasant dwelling”, maybe Valhöll, the famous 'Valhalla' the dwelling of the warriors dead in combat ?

Heimdall et Bragi are normally the warrior of Viðar (= Óðinn, or his son ). It is a bit hard to look at Loki as being 'Óðinn's warrior'. Bragi, however, is not at all a warrior. The poem thus carries here some ambiguity as whom might be going with Heimdall , is it Loki or Bragi ?

Fornjót is a giant's name. His sons practice the magic by which Óðinn's two warriors are carried away by a kind of stream. The word forn means 'ancient, pagan', and jótr is 'look, appearance'. Fornjót is thus 'the one of ancient look'.

Those going inside are 'obviously' the Gods, not the giants. Note however that the phrasing is unclear, as if the poet wanted, an in stanza 10, to indicate some confusion between the Giants sorcerers and the Gods.

We have also to notice how trifling the Gods look. They just failed in an important mission, and their first subsequent move is to join a beer feast. The poet is now obviously ironical, but we shall see this irony decrease later.

Fleeting irony and respect are typical of this poem, and of many Nordic myths. When Loki attaches his testicles to the beard of a goat, when Óðinn is so afraid that he lets some of the mead of the poetry escape “from the behind,” when powerful Thor is disguised as a bride, to cite a few occurrences, the Gods are ridiculous even though the circumstances are tragic. This feature of the poem should thus not be considered as not understandable.
        
18                
Heilan Hangatý,     Good health, Hangatýr,         
heppnastan ása,      happiest of the Aesir,        
virt öndvegis           the beer wort from the high seat         
valda báðu;              to lead they requested ;
[they requested (Hangatýr) to lead the beer wort (ceremony) from the high seat]        
sæla að sumbli         hapiness at the sumbel         
sitja día,                    they sit themselves the Gods,
[the Gods seat themselves in view of the hapiness of the sumbel (ceremony)]        
æ með Yggjungi       for ever with the young of Yggr        
yndi halda.                happiness they hold.        

Hangatýr , means 'hanged Tyr', once more Óðinn. This name calls on the suffering he imposed on himself in order to obtain runic magic. There are beer runes, where the word 'beer' certainly represents another word for magic. It thus the Gods have their little enjoyment with beer, and look ridiculous in light of the hard times to come, in appearance only. Calling Óðinn Hangatýr, reminds us of the beer runes, and that the Gods might also start a ceremony, where they use their own kind of magic, which depend on the runes.

A sumbel is certainly a ceremony full of joy, but not at all a drinking party. A horn full of beer or mead passes around, and each one drinks a gulp of it. Before drinking, however, a God is called upon, as in a classical (Christian) religious ceremony. The difference is that each one is a priest who drinks a small amount of alcoholic beverage.

Exactly as in a sumbel during which the mood switches from funny jokes to deep religious, the poem switches from mocking to respecting the Gods.


19                 
Bekkjarsett                 Bench sitted         
að Bölverks ráði          following Bölverk's advice,        
sjöt Sæhrímni              the family of Sæhrímnir         [the family of … Rakni,]        
saddist rakna;             sated of Rakni;         [sated with Sæhrímnir]!        
Skögul að skutlum      Skögul at the small tables        
skaptker Hnikars        form the long cask of Hnikar         
mat af miði                  measured the mead         
Mímis hornum.           of Mimir in the horns.        

Bölverk, the evildoer, is yet another of Óðinn's names. It begins a half-stanza that can again be mocking to the Gods. Sæhrímnir is a wild-pig the flesh that can never be eaten in full, and its family is a family of pigs. Obviously, poetical Old Norse constantly inverses the genitives in this way, and the exact meaning is given by the context. A kind of confusion is nevertheless underlined by the fact that Rakni is not such a famous person. He is a king of the sea, and his name is linked by the etymology to rögn 'the Gods'.        

Skögul is a Valkyrie described as a 'shield bearer' by the Völuspa she is thus a she-warrior whose role is protecting a male warrior. This, together with the next name given to Óðinn, Hnikar, 'the one who pushes the spear' changes the mood from joke to war in the second half-stanza.

Mímir's mead is the drink that brings knowledge.

The noun skaptker is read as skapker, a cask used to serve beer. It is also possible to think of a skapt, 'stalk, stick' to bring the feeling of a long cask out of which the mead can be served, hence my translation of skaptker by 'long cask'.

20                 
Margs of frágu         Much they asked        
máltíð yfir                 the banquet along        
Heimdall há goð,      to Heimdall, the Gods,        
hörgar Loka,             to Loki, the sacrificial stones,        
spár eða spakmál     foreseeings or clever words         
sprund ef kenndi,     whether the woman made known         
undorn of fram,        meanwhile forwards         
unz nam húma.        until caught twilight.        

In this stanza, Gods and Goddesses ask Loki and Heimdall until the evening in order to know “whether the woman (i.e., Íðunn- … - Jórunn) made known foreseeings or clever words.”

The word hörgr means 'heap of stones, sacrificial place, stone altar' and, in this context, it certainly points at the Goddesses. Here there is certainly an allusion to hörr, wax, especially since hör-gefn, the Gefn (one of Freya's names) of the wax, is a poetical equivalent to 'woman'.

In the Lokasenna, Loki boasts of having had sex with all the Goddesses. Our poem is either showing a devilish hint to the Lokasenna or at least underlining the fact that Loki was quite in favor among the Goddesses.

Note that Bragi is totally forgotten while, due to his role of official poet, he should be the one to tell the tale. This fact favors the hypothesis that in stanza 17, Viðar's warriors are Heimdall and Loki.