Videos not importing properly

Hey,

New to Davinci, i've been editing a couple of movies just fine, but today they are importing with a blank screen or a grey screen and not showing the video at all. The audio is working correctly.

The videos are .mov/mpeg4, 60fps, 1080x1080, 44.1 linear PCM 2ch audio. Approx 30 seconds long.

Some import fine, others don't. They are identical files though, same specs etc...

Specs -

Mac 10.15.7
Davinci Resolve - 17.2.1

Mac Pro 7,1
32gb Ram
GPU - AMD Radeon Pro 580X (8GB Memory)
3.5ghz 8 core Intel Xeon W

Any help or advice would be gratefully appreciated.

Thanks