Websites in Plesk are periodically inaccessible with 504 error: scoreboard is full, not at MaxRequestWorkers.Increase ServerLimit

Symptoms

• Websites in Plesk are periodically unavailable with one of the following errors:

  502 Bad gateway

  504 Gateway Time-out (nginx)

• The following message is repeatedly logged to /var/log/apache2/error.log or /var/log/httpd/error.log:

  CONFIG_TEXT: [Thu Jan 01 19:16:23.674685 2026] [mpm_event:error] [pid 3501586:tid 132589095683968] AH03490: scoreboard is full, not at MaxRequestWorkers.Increase ServerLimit.

• Apache version is newer than 2.4.7:

  #  apache2 -V || httpd -V | grep -i version
  Server version: Apache/2.4.68

  If Apache is on version 2.4.7 or earlier, check https://support.plesk.com/hc/en-us/articles/12377986768919-Sites-are-periodically-down-scoreboard-is-full-not-at-MaxRequestWorkers.

Cause

Apache scoreboard ran out of slots.

Resolution

Increase the ServerLimit Apache configuration directive accordingly:

How to calculate and adjust the MaxRequestWorkers limit on the server with Plesk