Unable to upgrade or equip convalescence spirit gem

I have a level 14 convalescence equipped and when I try to upgrade it to 16, I get the error "Operation could not be completed" and nothing happens. When I cut a new level 16 convalescence it doesn't let me equip it at all, despite me meeting the stat and spirit requirements.

I've tried:
- Turning off my other spirit gems
- Unequipping my other gems
- Buying a fresh level 16 convalescence
- Buying a fresh level 16 uncut spirit gem
- Relogging
- Restarting my game

After I deleted the level 14 conv I can still buy a fresh level 14 one and equip that, but I can't get any level higher.