404 errors on all websites

Symptoms

All websites on the server show 404 errors, and entries similar to the following appear in the Apache error log.

[Sat Oct 23 12:33:20.610279 2021] [:error] [pid 17733] [client 203.0.113.2:58246] [client 203.0.113.2] ModSecurity: collections_remove_stale: Failed to access DBM file "/var/cpanel/secdatadir/USERNAME-ip": No such file or directory [hostname "domain.tld"] [uri "/folder/"] [unique_id "YXPk8JHpCdES-kVD6hhC5wAAAAg"]
[Sat Oct 23 12:33:20.610595 2021] [:error] [pid 17733] [client 203.0.113.2:58246] [client 203.0.113.2] ModSecurity: Audit log: Failed to create subdirectories: /etc/apache2/logs/modsec_audit/USERNAME/20211023/20211023-1233 (Permission denied) [hostname "domain.tld"] [uri "/folder/"] [unique_id "YXPk8JHpCdES-kVD6hhC5wAAAAg"]

Description 

Enabling the "EXPERIMENTAL: Jail Apache Virtual Hosts using mod_ruid2 and cPanel® jailshell" option can cause unexpected 404 errors.

Workaround

1. Log into WHM as the 'root' user.
2. Navigate to "Home / Server Configuration / Tweak Settings."
3. Select the "Security" tab.
4. Scroll down to the "EXPERIMENTAL: Jail Apache Virtual Hosts using mod_ruid2 and cPanel® jailshell" option.
5. Set the option to "Off."
6. Scroll to the bottom of the page.
7. Click the "Save" button.

Additional resources

Tweak Settings: Security