I'm having a similar problem.
We have an event that was created before upgrade. I upgraded to DTRegister 4.1.0 and JAPayment Gateway 1.0.9. Then upgraded from Joomla 3.9.2 to 3.9.3. No error messages, with Joomla Error Reporting set to Maximum.
I created a new Field called "TEST" and saved it.
I opened the Event and clicked Save and Close.
The new field does NOT show up in the main list of Fields.
It does NOT show up in the event list of Fields.
It DOES show up on the form.
See screenshots.
I had to go into the database (through phpMyAdmin on our host) and Unpublish the field to get it off the Event Form.
Let me know if you need additional documentation of the steps I took. We'd appreciate any help you can offer.
Gretchen