I have Lightroom 6 running on a Macbook Pro with images, the catalog and previews all on an external drive. For no apparent reason, today the previews do not show up in Library mode. If I click on a gray rectangle and go to develop mode, the image is there and stays there when I switch back to Library mode. I tried "optimize catalogue", shutting down and restarting and cursing under my breath. Nothing has helped. Any ideas? Thanks
Have a read here-
Deleting the Previews file may correct the problem. The only downside is that LR will go a bit slower until it has re-built the Previews file.
That did indeed fix the problem the first, time. Now I need to figure out why I have to do this about once per week? Any ideas? Thanks
I am not technical, but sounds like your external drive may be corrupting the Previews folder.
Have you done any system checks on the drive? for bad sectors, etc.
Even checking that the drive has full read/write permissions for the top-most and 'included' sub-folders.
Checked for faulty usb cable or sockets causing intermittent problems?