Dear TIV.NET INC.,
>The htaccess code you show is settings for the permalinks.
Thank you for letting me know.
After I reset the .htaccess file, I did several other things:
changed the file’s permission from 604 to 644.
changed the permalinks/menu/category settings.
changed WAF setting of the domain.
and the site worked fine.
Since I also had other pluguin called “Site guard wp plugin”, now I think this one might have caused the problem, but not sure.
I still don’t know why the 500 error was caused, so I am afraid of it might happen again, but since I cannot find the cause, I reconsider the rating.
Thank you.