My thumbnails and timeline data went black; and this has happened seven or eight

Hi users of FCPX
I have had an ongoing problem that is damaging my trust in FCPX in business use and personal use.
Over the last 6 months I have experienced a disturbing and random loss of data in my library (and timelines).
My thumbnails and timeline data went black; and this has happened seven or eight times now in differing projects.
Now it is happening to EVERYTHING I import (audio files will sometimes remain valid in library).
Has this happened to any of you?
If so do you know what a solution might be?
I have already:
- closed and reopened libraries
- uninstalled and re-installed FCPX from app store
Thanks guys
Elliot

I've never seen this issue, it is not a known issue, there is some problem that is not common you are having.

Let's start with the basics:
• Hold both the Option and Command keys together while launching FCPX, which lets you delete the preference files.
• Once in FCPX, go to Preferences, and turn OFF Background Rendering.
• In the Browser, select the Library, go to the File menu, select Delete Generated Library Files, in there delete ALL render files.

Also, more info is needed to troubleshoot this unique issue:
What Mac model/year are you using?
What macOS and FCPX versions?
What is the capacity of your system drive, and how much of that is free space?
Where are your Library and media stored?