Swimming creatures without RunForward animations are motionless during combat
[Tested in latest Nightly, OpenMW-e524771b-Win64 released 2019-08-09]
Found another swimming creatures bug.
All creatures in the base game files that swim have a RunForward animation, and correctly use it when pursuing a target. However if a creature lacks this animation, rather than play no animation or use their WalkForward animation, they simply become motionless. They will still turn to face their target, and battle music will still play.
In the vanilla game the creatures will use the WalkForward animation (not sure if they move at running speeds with it, but it seems fast) and pursue the target normally. This notably affects the Cephalopod creature in Tamriel Rebuilt (ID: "T_Mw_Fau_Ceph_01" with newest Tamriel Data and TR), and probably other water life mods.
As noted, nothing in the base files that swims is missing this animation. I'm not sure if all creatures would have this problem as I can't think of any land creatures from any mods I have that don't have RunForward.