I would send an email to support@airtable.com so they can investigate your issue.

In the meantime, while you're waiting for a response from Airtable Support, you may want to try:

1. Creating a new interface form from scratch and see if it works.

2. Creating a form view and see if that works.

3. Creating a form in Fillout's advanced forms for Airtable. 

Fillout is 100% free and offers hundreds of features that Airtable’s native forms don’t offer, including the ability to update Airtable records from a form, display Airtable lookup fields & Airtable rollup fields & Airtable attachments & formulas on forms, dynamically & conditionally filter linked record fields by any values that you would like, perform math or other live calculations on your forms, accept payments on forms, create multi-page forms with conditional paths, create new linked records on a form, display as many fields as you want to see in a linked record selection list (including attachments), connect a single form to dozens of external apps simultaneously, limit the number of linked records that can be chosen, set advanced field validations & limitations, upload an unlimited amount of attachments simultaneously, add CAPTCHAs to your form, add choice matrixes to your forms, direct integration with hundreds of apps like Calendly & Google Maps on your forms, and so much more. 

Hope this helps! If you’d like to hire an expert Airtable consultant to help you with anything Airtable-related, please feel free to contact me through my website: Airtable consultant — ScottWorld

Interesting!  As a datapoint, I just tried this out and was able to submit an Interface form while not logged in just fine.  If you could provide a link to a duplicated version of your base with no data in it I'd love to poke around to see what I can figure out!

i find it more straightforward a publicly shared interface with an edit record link made with fillout.com

I am experiencing the same issue. I have tested (and at least five other people have tested) the form mutliple times this week. Today, during a demo, the message, "This form has been updated. Refresh the page to submit your form. Any information you already entered will be saved, but not submitted." appears each time the form is completed. The form is not in the interface mode, it IS in the upgraded form builder, it is shared publicly, and has worked over 20 times this week. There seems to be a glitch with the Done, Publish, and Submit functions. Additionally, the cursor is inactive (can't type) in the response fields on the form. Airtable has been closed out, and browser exited. "Accepting Submissions" is toggled on.  I also built a new form quickly and the same issues were present. I tested other forms (all built before the most recent form builder changes rolled out) and those forms work as intended.   As we are on the cusp of sharing the link publicly, this issue is very important.  Any help is appreciated. Thanks.