I've discovered this once on my own, I had a complex control remapper and that I had been evolving into a horrific bash hydra of hacks over many years. I briefly tried to get it working when I switched to Wayland. I don't remember which component broke me, but it went something like this:
"Hey, I wonder why doesn't this thing work in Wayland. I wonder if I can whip up a pale imitation."
10 minutes of stack overflow searches later...
"Oh... oh no."