I now can't access LR and get the message "LR encountered an error when reading from its preview cache and needs to quit. LR will attempt to fix this problem the next time it launches". Unfortunately it doesn't.
I have rebuilt the previews folder overnight and deleted the old one, but still I get the error when relaunching LR.
I know this reply is a little old, but I've gone through the same thing with LR Classic (Adobe CC, not the standalone perpetual licensed version). And it still comes up from time to time. Deleting the preview database and files is only a temporary fix, as the problem comes back later on.
So far I've been just using ACR/Bridge as the XMPs can be read by LR in the hopes that Adobe fixes this issue with the preview cache, or if I can find a way where LR won't create any previews at all, and thus doesn't need a previews database, which seems to be the problem.