Exporting .MOV issue

So I was given .MOV files to edit, which are the ancient file type codecs that Premiere wont let me use. So Ive been trying to open them in Media Encoder and export into H.264, It WORKS, however each time I export it within the first 20 seconds the video skips and then the audio de syncs during playback.

Its not my media player, Its definitely happening within Media Encoder during the export and no matter what I try, .MOV to H,264 conversion is glitching out and the files  are un usable.

Do we know why this is happening or how I can get around it?

File type ..MOV. 1080p 23.976 fps.