Google link shows 404 error but if i turn the seo off then there is no 404 error but it shows me my homepage instead of the relevant subject in the kuena forum. Web hosting allows .htaccess file to change the PHP settings. How to rewrite or solve this problem?

Hello all,

When i earch a subject in my kuena forum Google link shows 404 error but if i turn the seo off then there is no 404 error but it shows me my homepage instead of the relevant subject in the kuena forum. Why is the solution for that?
Can you please help me?

Google link shows 404 error but if i turn the seo off then there is no 404 error but it shows me my homepage instead of the relevant subject in the kuena forum. Web hosting allows .htaccess file to change the PHP settings