Cornerstone Form is not submitted when certain fields are shown based on conditions

Hello,
I have been using Cornerstone Forms and I recently encountered an error, with a form that has a redirect on completion
It has fields (required) that appear based on conditions. The form is not submitted and I cannot understand the error, as nothing appears on the screen (e.g. I get an error if a required field is missing, but no specific error if everything is OK and the form just won’t submit).

A similar (development) form is submitted perfectly (but has fewer conditions, and is set to submit via AJAX).

I tried changing cache settings, disabling plugins etc.

Could you please take a look?