Thorin's imprisonment "set right"

Question

In The Hobbit, Thorin and company are imprisoned in the Elven king's dungeons. After a time, Bilbo helps Thorin and the Dwarves escape, and the Elven king seems to intend all along to take some of Smaug's treasure, either as it comes back through the forest or via siege before the gates of the Lonely Mountain.

In Fellowship of the Ring, Book 2 Chapter 2, The Council of Elrond, Gloin complains that Thranduil's (the Elven king's) people showed him and Thorin's folk less kindness than they showed Gollum. Gandalf stops him, saying the Dwarves' imprisonment was "a regrettable misunderstanding long set right."

How does Gandalf think this was set right? By the Elves helping during the Battle of Five Armies? And Bilbo paid Thranduil back generously anyway. One can't help but feel Gloin has a point...

Answer 1

Besides fighting alongside the dwarves of Erebor at the Battle of Five Armies, as a concrete gesture, Thranduil returns Thorin's sword at the end of The Hobbit.

Upon his tomb the Elvenking then laid Orcrist, the elvish sword that had been taken from Thorin in captivity. It is said in songs that it gleamed ever in the dark if foes approached, and the fortress of the dwarves could not be taken by surprise.

This is a specific action on the Elvenking's part to "make whole" the dwarves, by returning what had been confiscated. No doubt had the other dwarves had specific property they wished returned, Thranduil would have complied (although none of the others had swords of any special value, as the group had not even bothered to arm themselves with blades until they encountered the trolls).

The elves also recognized Dain (and, retroactively, Thorin) as the rightful ruler of the domain of Erebor and valued neighbor. And while none of the dwarves were likely named elf friends, Bilbo was, which seems a clear indication that the escape from the elven halls had been entirely forgiven.

Answer 2

I always interpreted Gandalf's line as a gentle nudge not to dwell on matters already resolved - after all, with Bilbo's assistance the Elves and the Dwarves reached a settlement and fought together in the Battle of Five Armies.

Airing past grievances (however legitimate) seemed counterproductive to Gandalf, his main aim being to present a unified front against Sauron and not deal with minor squabbles between various parties at the Council, which might have endangered (or at least delayed) the discussion of the real problem, that is what to do with the One Ring.