I was playing on PS5 and had killed Greed in an Ancient Vault. A secondary Treasure Goblin was present, and was killed afterward because, as one might be able to tell, I had no resource and could not effectively attack. This was on Torment XVI.
https://imagizer.imageshack.com/img924/3087/sTIlRS.jpg [direct link as I cannot embed]
The error message did not appear to cause any actual issues – the Chest opened and I received the rewards but it was unexpected.
[edit since it won’t let me reply]
Also, this error (same general message but it does change some text) appears in Whimsydale upon X’ing (clicking) the gold pots and sometimes the happy clouds that drop gems.
Loot still appears but it is distressing to see “’!!MISSING!!” as if something is broken. This did not occur until the recent season patch.