I too have just started having this problem. (Chrome on Mac OS, PMS hosted on my Synology.)
Everything is fine and correct, but I just added my ginormous Looney Tunes collection into my Movies library, and some of them were matched incorrectly. After 3 or 4 “fix matches” working as it should, all of a sudden it just stopped working. Literally nothing happens. No window pops up, nothing tries to scan, nothing nada zilch. The menu just goes away and the Fix Match menu never opens. ¯\_(ツ)_/¯
UPDATE- Here’s a video of it doing nothing: https://youtu.be/KJha0kQn6A0
