Not trying to push an old problem but I just made a new world with a friend and the same issue I had last year is coming up again, I am using the newest version of both mods for 1.20.1 and after the game just randomly crashed I noticed that I got the same error in the log about the rocky roller and the bear crashing the game while fighting.. (I saw that it was marked as fixed, so I will try downgrading for the time being and see if the version around the time I made the issue does not have the problem.)

After testing the last version of the mod for 1.20.1 I can certainly say that it was not fixed... I downloaded the version from 3/5/24, the day after the issue was closed, and it didn't crash when I spawned a bear on top of the Rocky Roller, but it still crashed if they ended up attacking each other (I did this once again by going into survival, then swapping to creative while they both had agro and once they, even accidentally I guess, attacked each other, it crashed.)

I can't get this bug on 1.22.9 even when spawning a 20vs20 bear vs rocky roller arena, at least in my modpack.