I got the same problem today at
Plesk Obsidian v18.0.23_build1800200206.14 os_Ubuntu 18.04
for me the article from
Nov 11, 2018
solved the error:
mkdir /usr/local/psa/admin/htdocs/domains/databases/phpMyAdmin/tmp
mkdir /usr/local/psa/admin/htdocs/domains/databases/phpMyAdmin/tmp/session
chmod...
My Apache Version ist 2.4.29 and I get the same message. The Server was running a few years without restarting anything. For a couple of weeks I got the error "server reached MaxRequestWorkers". I set MaxRequestWorkers to 1000.
Now I get "scoreboard is full, not at MaxRequestWorkers. Increase...