One of my servers with apache 2.4.52 suddenly failed to accept connections. It turned out no child processes were spawned, only the main process running as root. Maybe related: https://bz.apache.org/bugzilla/show_bug.cgi?id=65769 https://svn.apache.org/viewvc?view=revision&revision=1896505
Seems to be other reported as well: https://forums.cpanel.net/threads/ups-421-apache-2-4-52-issues.696537/
Reproduced on second machine with 2.4.52 and MPM event.
Fix present in 2.4.53: *) mpm_event: Fix a possible listener deadlock on heavy load when restarting and/or reaching MaxConnectionsPerChild. PR 65769. [Yann Ylavic]
I've just added apache 2.4.53 to the tree, so this can now be tested.