I recently ran out of space so added a MicroSD card and moved photos and videos on the phone to it, and changed settings so photos and videos always go to the SD card.
Since then, or around that time, when viewing photos in the gallery, the old photos show up okay, but newer photos are blank with an exclamation mark and open as blank photos. Videos show the same but come up with a message about possibly not supporting the type of video file (mp4).
Auto upload to Onedrive is enabled and the photos can be viewed there okay, but videos will not play.
(Microsofy Lumia 550, Windows 10)