Can't save or edit events

Running Joomla ver: 3.9.2
JEM ver 2.2.3

Problem started occuring when I updated to Joomla 3.9.1 and JEM ver 2.2.3, can't save or edit events or cancel out of the edit screen. Using chrome tools I get Cannot read property 'task' of null at Object.e.submitform...at Object.e.submitbutton...at HtmlButton Element.onclick any ideas how to fix this? I need to get new events added and edit existing ones

Does the problem occur in frontend or backend?
Which template do you use?
Did you try to delete your browser's cache and load a new version of the page into your cache (CTRL+F5 or SHIFT+F5)?
It would be good if you copy the whole error message e.g. with line numbers if they are shown in your browser's console

I tested with the newest version of Joomla (3.9.2).

backend in as admin of the site.

Admin is using the standard admin template, never changed it. Frontend is using Kirigami from RocketTheme

yes, I've cleared both the server and my chrome browser.

JQMIGRATE: Migrate is installed, version 1.4.1
index.php?option=com_jem&view=event&layout=edit:377 Uncaught SyntaxError: Unexpected token <
jquery-migrate.min.js:2 JQMIGRATE: Migrate is installed, version 1.4.1
core.js?a56be189ad1318070e29af93039188fa:1 Uncaught TypeError: Cannot read property 'task' of null
at Object.e.submitform (core.js?a56be189ad1318070e29af93039188fa:1)
at Object.e.submitbutton (core.js?a56be189ad1318070e29af93039188fa:1)
at HTMLButtonElement.onclick (index.php?option=com_jem&view=event&layout=edit:237)
e.submitform @ core.js?a56be189ad1318070e29af93039188fa:1
e.submitbutton @ core.js?a56be189ad1318070e29af93039188fa:1
onclick @ index.php?option=com_jem&view=event&layout=edit:237

Those are the errors I'm seeing in the developer mode of Chrome

so no ideas what's causing this?

Get the same error trying to create a new category too. Creating events works fine

Sorry for answering late,
what I do not clearly understand: Does the problem occur in Frontend or in Backend (Admin)?

For more investigation I need more time