I am having similar (but may be different) issue. I am using v1.0.66.0.
I had exported configuration for a list from our on-premise SharePoint to SharePoint online list. I imported settings for view and edit, both imported fine and the form loads when clicked I try to view or edit a record. However, I am unable to go back into the configuration for these forms anymore. I see there are some errors in the dev console. I have attached a screenshot here.
So instead of importing the configuration for “New” form, I just created one default one. The form loads and I am able to go back and edit the configuration for “New” form as well.
It feels like the import may have brought in some old code that is messing with the way Modern DFFS works. The exported configuration had custom js and custom css in it.
Is there a way to remove configuration from a particular list form? I was unable to find that information as well.
