I figured out where I saw #202 in action: when rabbits flee from the player, as they do, they will willingly jump into tiny cacti. This likely coincides with their almost suicidal jumping from tall heights to evade players in vanilla, reported as MC-77732. This was tested with only Terrestria and the Fabric API loaded.

Since this might be connected to a vanilla bug, if you can't fix it, that's fine. I was simply told to let you know if I saw #202 again so the issue could be reopened.

I cannot reproduce this issue with one rabbit; rabbits can get damaged by tiny cacti but only if they are pushed into it by other rabbits, rather than pathing itself. Do you have a video of this issue?

I don't know how to make a video of it on Ubuntu without, like, screen capture software... It seems to only happen when they're running away from a player who is in survival mode, not creative. I went into a normal world, cleared out a 5x5 square of grass blocks, surrounded it with a one block wide square of sand in the ground with tiny cacti on top, spawned a rabbit in the middle, hopped in, and went into survival mode. It consistently leaped away, into the cacti where it meets its doom.