Hello, just a quick note to know if when building a form, the number of fields is limited. Indeed, I am unable to save the modifications of my form after having added fields during the deposit. It's weird the changes are not saved either in the "Administration" or "Site" tab.
I don't recognize that error. But have seen a content type get "locked" and not editable. It might be caused if you leave a form in edit mode for too long and joomla times out. Another possible cause might be if you have the same form open in multiple tabs. I haven't run into a field limit - one of the content types I have has 86 fields. How many fields do you have?
I usually end up rebuilding the content type when I run into issues. But there are a couple of thing to try before you go to that extreme...
Try removing fields until you can save the form. It might be a field causing the problem.
Another thing you can try is to export your app and import it into another test site.