I have done that, as advised, and it has not made any difference. Page attached.
Both tables have TINYINT fields which is what the checkboxes update. The page gallery-edit.php works and the page edit-event.php doesn't.
The only difference in the two pages is that in the Events table the TINYINT field has a default value of 1 whereas the Gallery table's TINYINT field has a default value of 0. This should have no bearing on the Update form though.
I have provided login details so you can see this happening online in the private message field below.