I had an interesting issue with LR today. I could do everything except export to a file (e.g. jpg). To cut a long discussion short, the answer was that it doesn't like my use of the SUBST command to shorten and manage different directories.
Example: If I have the command: SUBST Y: c:\user\alans\synologydrive\pics
Y:\Fuji\writablefolder is no good - I get an error in LR
but C:\user\alans\synologydrive\pics\fuji\wrtablefolder works just fine.
Photoshop doesn't have this problem. Neither does ON1 Photo Raw or Capture One.
Why do I do this? Because the data disk on my laptop is drive C and the data disk on my desktop is drive D. The 'synologydrive' folder (and sub folders) are synchronised between the two and I put my photos there. But so that Capture One can have a common catalogue, I've created a Y: drive which links to either C or D (depending on the hardware) and therefore I can look at the same files and edits on both systems.
Most of the time and with most programs, it all works fine. It's just LR that doesn't like this.
Anyway, it may help you at some time in the future, or this may be a problem unique to me.
Cheers
Alan