If you make model too large (too hight or to wide so bones wil be) or scale it to much your model will break (it`s possible if you made model in blockbench). For example my normal model


and scaled

CPM has a size limit of 25 on cubes. You have to split up the cubes in Blockbench.
You should use Pehkui to scale your model and not Blockbench, enable it in Effects/Scaling, this will effect the eye height and hitbox as well.