I’m not sure we need to go into that level of detail about how we build the App Clip, since the issue seems to be related to the App Store Connect submission page itself.
Every time I access App Store Connect, I can consistently reproduce the issue with the following steps:
Open the app submission page
Navigate to the App Clip section
Click on the Subtitle text field
App Store Connect immediately displays the error shown in the screenshot
If you think these details you asked is important, i can provide, but this looks like a App Store Connect platform crash.
Topic:
App Store Distribution & Marketing
SubTopic:
App Store Connect
Tags: