Thanks for those links Klojum. I didn't think there was anything I could do this end, but happy to help test any potential fixes.
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Update
I managed to SSH into my RPi3 and inserted the couple of lines that jakermx suggested and now the video plays, but it looks like it's upscaling a 320x200 video. Guess Ill have to wait until some people much smarter than I look at the issue.
Update 2:
Another reboot and all seems correct again. Thanks again Klojum.