It sounds like you’re opening an old catalog, one from before you moved the photos, if the editing you made to the photos is also gone.
One way this could happen is if you are somehow opening a backup catalog instead of your main catalog.
Have you gone out and verified whether your main (not backup) catalog exists where it’s supposed to and if that is the one you have open?
If you are just opening a backup catalog then opening the main catalog may be all you need to do. If there is no main catalog anymore then can you restore it from TimeMachine? I’m a PC person so aren’t sure what TimeMachine backups can and can’t do.
Thanks so much for your reply @ssprengel.
I checked everything you questioned and yes: the catalog is in the right place and the most recent one is the one that is opened (not one from a backup).
Now, I thought I had (almost) solved it: I used Time Machine to reset my Macbook to 5 or 6 days ago. And almost all the editing was back. That led me to believe that it was some temporary conflict.
This morning I opened LR5: and the same thing has happened again.. Most of the editing is gone, and LR cannot find some of the pictures (which I can manually retrace). By the way, this has happened to this summer's batch, my most recent editing work. The rest is not affected.. Still, this is giving me quite a headache..
Oh, I should add: the catalog is stored on my Macbook, but in the Dropbox folder. I'm going to try and find out if there is a Dropbox-synchronizing problem..
Like Ssprengel I'm not sure exactly how Time Machine works as I'm not a Mac user either but this does more and more sound like you've opened an older Catalog to me.
If it's not down to opening a Backup one then it does sound possibly like a Dropbox synch issue. I stopped putting anything other than temporary (and small) LR Catalogs in the Dropbox folder due to this very problem. Sometimes it just doesn't synch and comes up with an older file, though in my experience unless the file wasn't saved at all it does re-appear, usually with the name with a suffix that says something like "Conflicted copy". Are you actually using the Catalog on more than one computer during the time that this has occurred? If not then the Dropbox synch problem seems less likely to me (but not impossible).
Do you have a backup from the day you did the work to compare the one with the missing edits against?