u/Flat_Judgment1306

I'm hosting a public game with my partner; we both got this quest, but he went off and completed it without me.
The quest is complete in his quest log, but not completed in mine (and not showing as a "missed quest").
It's been a while, he's offline now, the terrain around the bridge pillar has come back; I dig down, and the chest is there, but opened/empty.

How can I complete this quest now? -_-