Animations not working with Optifine HD U G6/preview G7_pre1. They were working on previous versions of Optifine. I am using Minecraft 1.16.4, Forge 35.1.37. Custom mob models are from Overgrowth resource pack. The spiders will still walk on ceilings/walls, but do so right-side up. Expected behavior is that they are clinging to the walls.

If this can only be fixed by Optifine, I will try to open a bug there instead.

Same Issue but on Optifine HD U G6_pre1, i can provide logs if required, hopefully we can resolve this without optifine interference.

Yes, please also report this to Optifine. I'll do some testing myself later.

Confirmed this is working on 1.16.5 / Optifine HD U G7 pre4. @TheCyberBrick : I think this can be closed now

If you use the optifine version: preview OptiFine 1.16.5 HD U G7 pre4 then the animations work fine.
The optifine version looks stable as far as I have noticed.
 

Can also confirm on Optifine HD U G8 Pre1

Yes, I can confirm that the animations are working correctly on Optifine HD U G8. This issue can be closed

Closing issue, this is resolved. This is confirmed working now by myself and other users and to have been an Optifine issue.