Joomla: 3.9.19
PHP: 7.3.18
K2: 2.10.3
Template: Nano3, YooTheme

For some reason I am getting 404 Errors when clicking on all categories.
I do not get the errors when clicking on Items.

However, the links do seem correct:

-https://example.com/countries/chat-room/africa/angola/luanda

This is the error I get when I "inspect" the page:

- Failed to load resource: the server responded with a status of 404 ()

The categories do work if I DISABLE the setting called: "Enable custom SEF settings for K2 URLs".
After disabling the above setting, the category the link changes to the following:

- example.com/itemlist/category/94-luanda

I am NOT using anything like sh404SEF and my Redirect System Plugin is disabled.

A screenshot of my Joomla and K2 SEO setting pages are attached.

Any assistance on this matter would be greatly appreciated.