AppleTV no video (just audio/subtitles) on BritBox, ITVx, Prime

Started having issues today with BritBox, ITVx and Prime apps on AppleTV 4K. I have audio and even subtitles, but there is no video. If I access the same apps directly from my LG smart TV the issue does not occur, so it is definitely an AppleTV issue. Strangely, it was working fine earlier in the day, but after stepping away and coming back the issue started. I have updated all relevant software (including tvOS) and rebooted the AppleTV multiple times.