WordPress permalinks with the category and the postname throw a "Page Cannot Be Found" error

Question

Background: I have developed and managed many WordPress sites over the years. Only one of these sites has this problem, but, based on comments on the WordPress.org forum, others are having the same problem. So far, I have not seen a solution that works.

Problem: Links work with the default setting. This setting does not add a .htaccess file to the site. The addresses look like ?page_id=12. Permalinks with just the postname also work fine. But permalinks with the category and the postname throw a "Page Cannot Be Found" error.

WordPress Permalink Options:

1. Plain - default, no .htaccess file created

2. Day and name - just a radio button choice

3. Month and name - just a radio button choice

4. Numeric - just a radio button choice

5. Post name - this is the equivalent of adding /%postname% in the 6th option. This one works.

6. Custom structure - the code I prefer to use is /%category%/%postname%. This one does not work on this one site. This code does work on all the other sites I have added it to.

Environment:

• The site is hosted on SiteGround.
• The site is running WordPress 4.6.1
• The site is using the Matheson theme.
• There are only 9 plugins that have been checked for being up-to-date.

Answer 1

Switch to a default theme and see if that permalink structure works or not. Outdated themes can cause issues with newer WordPress versions.

Then after this, try to deactivate one plugin at the time and check the links. One or more plugins are in conflict with structure.

Structure where you have just %postname% will work.

Answer 2

You should have no problem using the /%category%/%postname%/

Maybe try checking through your other settings on the sites it does work on and see if you can find something different that may be disabling it or hindering it from functioning the same as your other sites.