This seems to be an issue with WordPress 6.1
After WordPress 6.1 update, If your website is down and in the apache error log you get the following error:
PHP Fatal error: Uncaught Error: Call to undefined function cache_users()…
Then we’ve 2 solutions to deal with solutions:
1. log in to your cPanel or access the plugins folder through FTP. Then rename the plugins folder to plugin1 or something and create a new plugins folder. Then log in to the wp-admin panel and try installing plugins one by one. You’ll find the culprit plugin. Ignore that plugin and keep using the rest of the plugins.
2. This solution needs modification of the CORE file.
comment 79th line in /wp-includes/class-wp-user-query.php(79)
That’s it. It’s a temporary issue until the WordPress core team pushes the new update.
Hope this helps. If you need any help (Paid), please drop an email to firstname.lastname@example.org