The sheer number of domains is not the primary issue. A server could have lots of domains that do not receive much traffic or which have only static web sites.
The issue here is that the web server (httpd) has failed and load is high. Support is normally alerted automatically to such issues. If it continues for 30 minutes or so and you don't see anything in the server announcements forum, you could open a Support ticket.
I am not WHB staff and I am not paid.
I provide help in these forums on my own time.