I had the same issue. I used Shotcut and handbrake to make sure the video met all the requirements but still ran into this problem. I did upload from a mac mini and was using Safari. I had left it like that and was able to submit to Apple but the videos don't appear on the app store page. So I tried again to make sure I could play the videos before I submitted. Unfortunately the only way I got it to work was to upload and remove multiple times until it worked. Felt like hours. I know this isn't the solution anyone is looking for but I thought it was worth mentioning that it does eventually work. I did leave the video for the iPhone 6.5" uploaded in a similar state over a weekend and was working afterwards. Once they worked I was able to preview the video and play them on the website before submitting to Apple.

If anyone is having the issue in only sandbox enviroment for their apps it could be related to an ongoing issue with the sandbox at the moment. I reached out to apple and they said they are currently working on it. For those looking for updates to the status go here: https://developer.apple.com/system-status/ hope this helps

Same issue here, only subscriptions seem to be affected but no changes have been made. Reached out to apple for support.