Unable to Submit for Review - This field is required

I am trying to submit a new revision of an existing free app to the App Store through App Store Connect. I have filled in all required field, but when I press the "Submit for Review" button, I get an error message:

Unable to Submit for Review

The items below are required to start the review process:
This field is required

There is no indication as to what field is required and I cannot continue. The problem never existed before.
I needed to specify a copyright field.
Found the error! I could submit now!
The copyright field is now required!


This must be new! Didn't have this problem two weeks ago. Wished the error message would have been clearer!