Running a site with custom logins and custom post types, we are finding that the permalinks need reset every 3-4 weeks.
The symptom: The site will begin dropping 404 errors and the .com/login is now a 404.
The fix: Comment out the custom function for the login redirect so we can access /wp-login.php, proceed to reset permalinks, then un-comment the function.
Server: Digital Ocean with Ubuntu build, 32gb ram. WP 5.x, with Woocomm, Sensei, ACF, and a dozen more common plugins.
The question: Why would a high traffic, high use site drop permalinks over time with no changes of code, post types, or plugins?