At this time, we believe this bug is related to having the Ring of Entanglement equipped to companion(s) who are inside the endgame fathoms. We are actively investigating this issue to address for a future update.
As a work-around, you can try to load an earlier save file and remove the Ring of Entanglement from your companions and the Last Castoff, and see if that resolves the issue.
This issue should be fixed as of the 1.1.0 patch, but you may need to load an earlier save file for the issue to resolve in your game.