Joomla! 3.9.21 Stable [ Amani ] 25-August-2020
K2 v2.10.3
PHP Version 7.4.9 (upgraded from 7.3.x which also had the issue)

In the back-end, when I Save and Close for an item, I get the error message 403 You are not authorized to view this resource.

When I merely Save the item, it all works fine. I know I can then Cancel to get back to the list of items but I need to resolve this issue for a client.

I am using a couple of K2 template overrides but I've turned them off the error persists.

I am also using Helix Ultimate template but similarly, having defaulted back to Protostar template and the error persists.

I am logged in as Super Admin and the client is logged in as Admin.

I have the latest version of Admin Tools installed and have ran the Fix Permissions tool and Reapis and Optimise Tables (for good measure).

None of these things have made a difference.

Anything else I should be trying/checking?

Thanks.

Andrew

This issue is continuing and i have more problems as well.

I have a fuller post:

www.joomlaworks.net/forum/k2-en/57228-an-appropriate-representation-of-the-requested-resource-could-not-be-found#178041

Other parts of Joomla are not affected.

I am able to save and close other pages within Joomla - including template pages.

Thanks

Andrew

The 'cross post' was because additional issues have subsequently occurred which may, or may not, be related to the initial issue I raised.