[Plugin: Custom Permalink] Page navigation – Error 404

I have set the permalink structure to /%postname%/ and installed Custom Permalinks plugin. This plugin is working fine with custom category permalinks.

For eg., https://example.com/sub-category/sub-sub-category/ is correctly redirected to the custom url https://example.com/sub-sub-category

BTW, I have used WP No Category Base plugin to remove “/category” from the category permalink.

Problem:
The custom category page is not working with page navigation (using WP-PageNavi). It gives me “Error 404” on clicking page 2 or any other page from the navigation links.

Please take a look at the error page – https://bit.ly/3okOGm

The page navigation works fine when “Custom Permalinks” plugin is deactivated.

I tried Category pagination fix plugin. It does resolve the problem when permalink structure is set to “/%category%/%postname%/”. But, I want the structure to be “/%postname%/”, so that the url of post doesn’t contain category names.

Could someone please suggest a fix for this problem.

Details:
Wordpress version : 2.8.5
Theme : K2 child theme
PHP Version : 5.2.6
MYSQL Version : 5.0.51a-24-log