Why MOV causes compatibility issues
MOV is common for Apple and camera workflows, but some upload forms, older devices, and non-Apple apps handle MP4 more reliably.
Convert MOV to MP4 first
MP4 is the best first fix when a MOV file will not play, preview, or upload. It is broadly supported and usually accepted by social and web platforms.
After converting
Play the MP4 from start to finish, especially if the MOV came from a camera or editing app. Check audio sync and orientation.