HI there,
The best approach I would suggest is turn on some network traces to get the details of failure, there you will be able to confirm the missing fields.
Developer tool from browsers, Network option is great for it.
In addition to that, I would suggest to :
- Test other forms if the failure happens
- On form editor, expose all the hidden fields and check which one is mandatory but not filled.
-Disable all custom javascript codes from all forms
-Evaluate a trial creation, so you can compare what is native and what is missing