To find out what is causing the problem, enable logging on your WordPress site.
The wp-config.php file should include the following lines just before the line “/ * That’s all, stop editing! Happy blogging. * /”:
define ('WP_DEBUG', true);
// Enable Debug logging to the /wp-content/debug.log file
define ('WP_DEBUG_LOG', true);
/ * That’s all, stop editing! Happy blogging. * /After it, reproduce the 404 error and see the fatal errors on your wp-content/debug.log file.
After finding the cause of the problem, we can move on to the solution.