This happens when we upgrade clouds and in some cases, a dedicated IP or an account is not synced yet. The fix is easy though, just add a /cpanel after your domain. For example, if your domain name is:
your-main-domain.com
You can access cPanel directly with this address in your browser.
your-main-domain.com/cpanel/
You can also do this with the Web Host Manager or Webmail like this:
your-main-domain.com/whm/
your-main-domain.com/webmail/