The "By Minecraft" "STAR WARS" Texture pack included in the mash up pack has almost all mob textures bugged and been like it for a couple weeks now which is quite long. Wierd white or black boxes covering details and just completely buggy looking texture please fix Minecraft thanks 😄👍 first bug report so sorry if I've not made anything clear. Me and my friend have the same bug on different devices on each of our own worlds.
Based on the item you're holding, you have some other resource pack enabled. Does the issue still occur if you disable that pack?