AH00288: scoreboard is full, not at MaxRequestWorkers

Symptoms

Sites load slowly when visiting them, in some cases taking 2-3 minutes to load or timing out completely.

Receiving the following error in the Apache error log:

[Tue Sep 29 18:27:12.072221 2020] [mpm_worker:error] [pid 15422:tid 47647048848448] AH00288: scorebo
ard is full, not at MaxRequestWorkers

Description 

When the Apache scoreboard is full, no more new connections can be made and pending connections must wait until an existing connection closes to be able to connect to the server. This can result in slow loading times and time out errors.

This is a known bug in Apache versions before 2.4.7:
https://bz.apache.org/bugzilla/show_bug.cgi?id=53555

cPanel uses the latest official version of Apache, which is version 2.4.46, and thus it is still susceptible to this bug.

Workaround

Currently, there are two known workarounds:

1. Switching to MPM Prefork

2. Configuring logrotate to restart Apache instead of reloading it and increasing the MaxRequestWorkers limit

You can read more about tuning the MaxReqeuestWorkers limit here:

https://support.cpanel.net/hc/en-us/articles/360047992273-Tuning-MaxRequestWorkers-for-Apache