In version 1.22.5 Laviathan's speed seems to be broken. While in lava it moves extremely slow when ridden by player. While on land it moves way too fast when ridden by player. Its speed in water seems to be ok, however, it occasionally stumbles on something invisible which forces it to change direction slightly ( this particular issue is manageable tho). It seems to me that for some reason its speed on land and lava got reversed. I don't think that this issue is caused by other mods but I am playing BetterMC4 modpack for 1.20 so there is a tiny chance of that being a case. Anyway I hope it gets fixed ASAP cause its one of my favorite mounts for nether.

Also Laviathan starts drowning in lava if the player doesn't move while riding it