I have been having this problem for quite some time with the 1.12.2 versions of More Player Models. Whenever I change anything with my character it doesn't actually change, for example, I changed the size and my view changed but my character remained the same size. Animations and movements also don't work, once again if I try to sit it changes my view, but my character is just standing with their feet slightly in the ground. I am using other mods with this, but not anything I think would affect it. The mods are:
chiselsandbits-14.33
CMDCam_v1.4.4_mc1.12.2
CreativeCore_v1.9.66_mc1.12.2
CutsomNPCs_1.12.2-(01Oct19)
Decocraft-2.6.3_1.12.2
DoggyTalents-1.12.2-1.15.1.4-universal
mclib-1.0.3-1.12.2
MorePlayerModels_1.12.2-(05Dec19)
pa1.10
PTRLib-1.0.4
Any help would be appreciated, thank you.