Its exactly what the title says, the rocky roller has issues with the bear from untamed wilds which in turn crashed my server (it is not a server problem as it crashes any world as well). Here is the log. (I posted a comment on an issue about mod compatibility on the untamed wilds page but I thought it would be worth putting it here as well, I also ended up posting a new issue about it there as well as the issue I commented in was very old).

So this seems to happen when they collide with each other. I'm not exactly sure why or which mod is causing the other one to break to the point of crashing the game but the easiest way to recreate this bug is as followed; download alexs mobs and untamed wilds for 1.20.1, open a new game (a superflat creative world is fine for testing this). after that either; dig a 3x3 hole and spawn a rocky roller in the middle of the hole then spawn a bear on top of it, (this will work with any type of bear that is spawned in). or; spawn a bear and a rocky roller then go into survival mode while the bear is between you and the rocky roller and then go into creative mode again so they fight, that will eventually cause (what I believe to be) the same crash.