Just started getting this error today, not sure what causes it. Doing various things seems to pop it, waiting through the end mission details for loot got it once, turning in quests as well.
Server error: backend error 1110. Or some such as that.
As a side note, I did lose one of the loot chests…as it dropped as we finished Skittergate legend and so I got no loot, I did get the achievement at least.