Missing elements of prefabs

Hello!
Recently had a problem. Please help!!!

The project was made in 2019.2.11f. Looking at renewed interface updated the project to 2019.3. Found that some parts of 3d models (elements of prefab) are missing.
Tried several approaches to fix.
The most 'heavy' was in total uninstalling and installing back Blender (even in case that parts of model missed in fbx). Uninstalling and installing back Unity with hub. From 2019.2.11f to newest 2019.2.19f
Didn't help.
What could save situation?

Except manual looking for missed parts. Possible but could take too long.
And besides it is more useful to find out root of problem. To avoid it in the future.

Can anyone assist?
Thank you!