Some models (wolves for this example but also noticed this with the cats with tuffed ears) have missing textures. Their .png file also support things missing/hidden. Not sure what could be causing these issues if they are on my end.
I am currently playing on Minecraft 1.12.2 (1.12.2-forge1.12.2-14.23.5.2847). Current version of Animania and its addons. Singleplayer

Default wolf0.png file without edits:

Default wolf ingame:

Edited wolf0.png to see transparent issues:

Edited wolf ingame: