Hi Chips,
I realise it is not ideal but is it possible for you to upload a video to iCloud, Google Drive, Dropbox, YouTube, etc. and provide a link to show what the issue is?
Additionally, just a few related questions:
- have you got a complication running full screen at the time this happens or just a watch face
- has your watch been in direct sunlight for long and does it feel hot to the touch
- have you updated to the most recent WatchOS release / are you running a WatchOS beta
- what is your battery charge (approximately) at the time this is happening?
- what is the brightness setting on your Always On Display (default, low, high)
Unfortunately the possible causes are still fairly broad at this point - it is entirely possible you are having issues with the ambient light sensor, or it could be related to operating temperature, etc. I would also suggest biting the bullet and doing a pair and unpair and a clean set up of your watch just to eliminate setup/connectivity as potential factors.