I do not see any error/issue with UFW.
My guess is with the widgets and other forms which you have inserted on the “register” page.
There should be some conflict with registration form and other forms present on the page.
You can try disabling widget box one by one and see which widget is causing the issue.
If you can use the “PRO” version of the plugin, you can set rules on which page you want to insert the widget box.
You can also edit the code in plugin editor –> ultimate floating widgets –> includes –> display.php and insert below line at line no. 27 to stop the widgets from being put in that page.