Visit your website, few pages. Eventually you will encounter infinite loading and timeout.
Maybe related, error.log contains:
2021/02/13 10:17:53 [alert] 31891#31891: *330 open socket #37 left in connection 8
2021/02/13 10:17:53 [alert] 31891#31891: *329 open socket #35 left in connection 9
2021/02/13 10:17:53 [alert] 31891#31891: aborting
When enabling mod_security there is strange problem with connection. After enabling it, few minutes latter all connections timing out.
It is easy to reproduce:
Maybe related, error.log contains: