You have a complex solution, and when you press the submit button it will tell you that it cannot be submitted as the validation has failed but there are no fields flagged.
The fields are very likely hidden fields.
How can you tell which fields have failed the validation checks when you press submit?
Composer 11.x &12.x
Error in form.
The below should give you a list of all validation errors and field names even if they are not on the form.
If it is a relatively recent version you can do the following:
(1) Submit the form.
(2) Press OK in the validation error Pop-up
(3) Press F12
(5) Type this in and press enter: $form.errorInfo
(6) Expand the result by clicking on it