highlights on pdf using preview disappear on the files continuously.

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode?

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

I doubt much will be fixed in Catalina from here on out.

Take a couple hundred million people with you over here...

https://www.apple.com/feedback/macos.html

Any luck yet?