Custom entity models not loading properly once imported (models created in Cubik studios)

Hi there, I have been making custom java models using the tool Cubik studios and they seem to import fine into Mcreator. However, when I try and test mod these custom mobs do not form properly. For example the different elements don't connect, sometimes the legs are missing, sometimes they are sunken into the ground, etc. I was wondering if anyone else has had this problem or might know how to fix it.

Thanks.