only characters become invisible on android build.

I am building oculus go 3d travelling experience.
everything seemed fine on export but strangely all my avatars (characters) become invisible.

I imported characters from several diffrent sources (unity, iclone) everything is ok in editor.
But after build ony characters get dissapeared. guns in their hands stays on. A camera, child of a main walking character becomes activated and travels along with the character. just characters seemed vanished.

I build for both cardboard and oculus go and yet only tested on my mobile phone.

Any ideas.