If you're having a problem with your WordPress installation, there are a couple first steps that you can use to determine what is causing the issue.
Disabling your .htaccess by renaming it to .htaccess_old will allow you to test your site without a functional .htaccess file. If your problem goes away, you know that the .htaccess was the culprit. Further examination of your .htaccess will help you isolate the cause.
Disable plugins & themes
Disabling your plugins by renaming the plugins directory to /plugins_old/ will allow you to test your site with your plugins disabled. If your issue stops, you know one of your plugins is the cause. The next step will be to rename the directory back to /plugins/ and begin renaming each individual plugin folder one at a time to isolate the culprit. You can use this same tactic with your themes directory, by renaming it to /themes_old/. If the problem disappears you know it was your active theme.
If you're still having trouble after trying these options, we're happy to offer our input - just hop into chat or open a ticket!