Conversational form, having to press "Submit" twice

We are experiencing an issue with the Conversational Form where clicking "Submit" greys out the button (as if it is submitting), but after about 10 seconds the button returns to the original state (without the form submitting). Pressing the button again then submits the form successfully.

Could anyone advise on how to resolve this?

Stack: Bricks Builder, ACSS, Fluent Forms Pro