Maybe someone can offer some advice.

Since the models disappear for random heroes, I would attribute it to scripts – some script with an error removes the hero models (but this is just a guess, I don't know much about scripts).

We could consider the possibility of an issue with the model's script, but I changed it to a completely different one, copied it from a hero where it works, and it still has the same problem. The hero I copied it from is fine, but this one is in invisible mode, haha.