The way you have your a2.php set up, it is filtering a recordset based on a $_POST['recordID'] value from the first page. The update is set up to update the record displayed in the recordset.
However, after the submit, the $_POST['recordID'] value will no longer exist.
The easiest solution at this point is to add a hidden form element name="recordID" and set its value to the UserID in the recordset so it will persist when the form submits again.
I'd also update the trigger value in the update server behavior to use the button press event instead of the current page submit. Current page submit verifies it is the current page from the referrer in the header and that can sometimes be blocked.