I also went ahead and submitted a bug report here: FB22317839

There is also another thread about this here: https://developer.apple.com/forums/thread/820074

This is happening to us too. The app store connect UI wiped all of our existing app clip configuration (image, subtitle, title), and trying to upload a new image to fix it doesn't work, nothing happens in the UI. Tapping 'subtitle' shows the same error as the original poster. It also blocks us from submitting a new build, since the UI complains about the app clip fields being required.

Same issue here. Attempting to edit any app info field doesn't work - and our existing app clip information has all been wiped.