Convalescence Spirit Requirement Bug

THANK YOU SO MUCH!!! THIS WORKED

Just wanted to add my own experience:

Apparently Ravenous Swarm also counts for this issue.
I deactivated it for Slot 2 and Convalescence worked.

I am having the same experience. I have the same equipment set to both weapon sets and more than enough spirit to run it. It even lets me activate the skill, but I can't actually use it. So it is reserving the spirit but is unusable and is not telling me why.