This has happened to me twice. The first time I fixed it by deleting all the hotbars but one, then putting them all back, deleting the one left behind, and putting that back.
The next time it happened I either borked it myself or the bug was worse - either way I lost my hotbar setup entirely (and hadn't saved it..
), and had to delete the UI file for that character and start again. I hope and pray you don't have to do that.
This was way back with the early ProfitUI, so YMMV...