Never saw this before. I imported a new shoot and lost an entire set of a locate/pose/outfit. A later set from the same shoot—just different location and outfit—duplicated and then replaced the photos. However, the ones that duplicated and replaced didn't retain the minor, global changes (white balance, exposure, etc.). Luckily, my iMac is set up to backup the photos as their downloaded from the camera.
That same overall set of photos (not a lot, just about 126), continued acting strange. I'd selected two photos and worked on them. After quitting and reopening (thinking it might help), I'd select a photo to view. Next, I'd use my right/left cursor to move to the next photo and a different photo from down the sequence would jump into its place. Photos were out of sequence, too, so that the various poses/outfits/locations were shuffled like a deck of cards. I never could figure out how to reorder them as they were before.
Eventually, I created a new Library by Importing them again, changing the name. It's what I'm using now and all is working fine. I'd like to figure out if it's something I did that caused this. I remember toggling Library > Enable Filters. Just now I opened up the "bad" catalog, and just L/R with the cursor, images that *were* horizontal/landscape were flipping to vertical/portrait. I can see the strip at the bottom of the window and can anticipate the next outfit/location, but when I L/R cursor to that image, it pops up on the screen for 1/2 second, then it's replaced by another image. Almost like it's recording based on when an image was last opened?
Thanks in advance!