I had the same issue, I had to re-load a previous save (12 years earlier) I get around the problem, not sure what caused it.

Thank you both! Thanks to your insistence I found the bug and corrected it: you couldn't enable a mint in a barony you held, but you could in baronies of vassals or below, that's why I thought it worked. I forgot to add a trigger.

I was convinced that your complains were an issue with the holder not fulfilling the condition "completely_controls" county, because I remembered counties having a control "complete" beyond 100. It looks that it isn't the case now, the maximum appears to be 100, so either I misremember or something has changed in one of these past updates. That was not the issue, though.

Great news ! Thanks again for your work !