Maybe if you append them? In the file menu.
I need to try this
No.It didnt help
Sorry thats the only idea I had, hopefully someone else might have an idea.
Could You share blend?
whats Your hardware? Maybe it is hardware related display problem?
it says file is too big… Let me upload to g.drive
Mmm… Thanks for ur help. I think its an issue in set up then. I should try other version of blender
I believe this is a bug involving objects with multiple materials, which I encountered myself. I read that it was known, and supposedly fixed… but it doesn’t seem to have been resolved, according to your experience and my own. 
I found blender’s 2.8 version again and solved it. Other people told me that my b.2.81 is broken cuz when they open my file it was not broken. Anyway i solved and will not go over 2.8. thank you all

