Once the Animation Toggle debug option is turned on ( F3 + O ) some pokemon appear to not be loading the first frame of their animations properly and instead just using the T-Pose, i saw it happen with a Sinistea, Murkrow and Hoothoot, i believe there were others, but i could not tell, if it helps, i had Rubidium and Magnesium/Rubidium Extras, at 3 render distance

Greetings,

The Animation toggle option simple stops all animation. So if they were in mid wing flap or walking stance, they'll remain like that. It isn't designed to reset back to frame 1.