I just checked my MacBook Pro, which is still on 12.2.1 but otherwise configured the same as the Mac Mini (it was set up from the MBP), and it reports ‘VASSAL Module’ for Kind. Perhaps it’s a 12.2.1/12.3.1 thing. I’ll be updating the MBP soon, so will keep an eye on it.
MBP updated to 12.3.1 and it still reports ‘Vassal Module’. Looks like there’s something with the config of my Mac Mini, although I have no idea how/what/when, or what the fix might be. Meh. Nothing to be done on the Vassal side.