Possible corruption on flash drive
Fix common problems tests the integrity of your flash drive by ensuring that certain required and guaranteed to exist files can be correctly read. You will see this error if these files are missing and/or cannot be properly read.
Reasons for a corrupt flash drive could be:
Unclean shutdown caused by power failure, crashes etc when the server is possibly updating information on the flash drive
Defective flash drive (replace it)
It would probably be best to create a post in General Support and include your diagnostics for further investigation
NOTE: This is a relatively new test and there may be some false positives due to various configurations, plugins installed etc. If a false positive is found, then the next release of Fix Common Problems will "whitelist" the configuration file.
If you have any questions, post the full FCP warning and your diagnostics (from Tools -> Diagnostics) to this thread https://forums.unraid.net/topic/47266-plugin-ca-fix-common-problems