Project stages suddenly going to "undefined" instead of the selected stage

Question

Pretty positive this was working fine earlier this week. When I click on a project task in Kanban view, then use the stage named arrows in the top right to move it to a different stage (specifically one I can't see in Kanban view because it's currently unoccupied), the arrow doesn't turn blue, and the project stage is just dumped into "Undefined."

I double checked the numbering sequence of my project stages, and they're all intact. Not sure what else it could be. Suggestions?

Edit: This is als

Fabrice Henrion (fhe) · Accepted Answer

Are you absolutely certain that your project lists the stage you want to move the task into?
To verify this, go to Project > Configuration > Stages, open the stage you want to move the task into, verify that your project is listed in the section "Projects using this stage"

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