In the newest version of the mod, after getting sucked by a lamprey, even after killing it, every time after landing with elytra after flying for long enough to cause wear on it, a lamprey spawns in and instantly dies. You don't take any damage, but it is fairly startling.

I am also still experiencing this issue on 1.12.2-9.0.1

1.12 is no longer supported for bugfixes, so the chances of this being resolved are near 0. You can ask @bglandolt to add it to Better Animals Plus Plus, perhaps.

Managed to reproduce this in 1.12, and I've fixed it. We'll see.

Please follow the issue format. What MC version, mod version, etc.

I'm experiencing this issue still, version 1.12.2-8.1.1.