Do I have to reboot the server after initializing quotas on an XFS® filesystem?
Yes, it is mandatory for the server to be rebooted for the Quotas to be initialized after enabling quotas on your server—the last change needed for rebuilding the grub configuration file used during the server boot procedure.
You will need to complete all the steps mentioned in the following guide:
You may need to run the following to see the quotas set for cPanel users.
More details can be referenced here: How to Fix Quotas.