Part of animated mesh ignored by spotlight

I have a issue with a model that was splitted into four submeshes on import. The last of these submeshes does not get any light from a spotlight. Not sure how to fix it or where to begin searching.

I made this gif to show the problem:



So, all submeshes use the same material. Any idea what could causes this behaviour? The model produces also no shadows. This is a vr-project.

[Unity 2017.1.1f1, Win10 64 bit, Nvidia 1070]