I feel like I've scoured the internet looking for an answer to this -- short of uninstalling but I'm hopeful there is another way. I've recently subscribed and started learning Lightroom specifically to organize my photos better. I watched a full course on lynda.com and then began the process of gathering photos, organizing them in explorer, then synchronizing. Once synchronized all changes henceforth would be made in Lightroom ideally. So I started. I synced thousands of images so far. However I just noticed that it did not sync all of the folders in my 2015 folder. It does recognize them because when I go to sync again (as seen) they are all grey and there are the smart previews (or catalog? idk) thumbnails shown. I restart my computer. I backed up the catalog before doing so. I'm unclear on how to clear out a catalog if that could somehow fix this. I'm nervous to continue on if this becomes a recurring issue.