I use Joomla Version 3.8.6 with "The ALLROUNDER 3 - Joomla Template" in Version 1.1 and I have a problem when I edit an article via frontend. When I want to save the article nothing happens. All other buttons (close, etc...) work correctly.
In my browser console I get this error message when I click on the save button:
> Uncaught TypeError: Cannot read property 'isValid' of null
> at Object.Joomla.submitbutton (index.php?view=form&layout=edit&a_id=1&catid=8&return=aHR0cDovL3Rlc3QudHNjLXpldXpsZWJlbi5kZS9pbmRleC5waHA=:67)
> at HTMLButtonElement.onclick
This error happens for all different types of users (Editor as well as Super-Administrator)
I deleted the template completely from my webspace and did a new clean install but the error is still there. I tried to disable Jquery-Scripts in the header as well as all other Javascripts but this did not help. I also disabled sequentially all plugins, but the error was still active. Further, I set up textfilter for all users to "No Filter", but the error was still active.
Thank you for your help!