Issue Random concurrent issue with Apache / Nginx service down on subdomains

[elderbre]

I run a website through a dedicated server with Plesk Onyx and for the last few months, the service on a single subdomain would suddenly go down, although all monitoring showed no problems on the server and other subdomains working normally.

I installed Watchdog a couple weeks ago and it would detect when Nginx would go down and restart it on it's own, however today Apache also went down along Nginx on a subdomain that usually never goes down and the main domain (although other subdomains worked normally).

Due to server monitoring I know the server is not having issues, and other domains are not having any problems while the service is down on the specific subdomain having the issue. I have been playing with the settings of Nginx and Apache to no avail, increasing their resources through workers and capacity just in case, but this did nothing.

I am a bit lost at this point on what to do, other than getting a new server and transferring everything to see if the problem goes away.

Apache log isn't very helpful on what may be going on... it just notes that Watchdog asked for a restart:

[Thu Jun 28 21:05:34.081088 2018] [mpm_event:notice] [pid 29370:tid 140609184798848] AH00492: caught SIGWINCH, shutting down gracefully
[Thu Jun 28 21:05:40.171376 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29443 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:40.171395 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29444 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:40.171402 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29446 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:40.171407 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 30150 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:42.435893 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29443 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:42.435914 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29444 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:42.435919 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29446 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:42.435924 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 30150 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:44.437981 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29443 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:44.438002 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29444 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:44.438008 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 29446 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:44.438013 2018] [core:warn] [pid 29370:tid 140609184798848] AH00045: child process 30150 still did not exit, sending a SIGTERM
[Thu Jun 28 21:05:46.440066 2018] [core:error] [pid 29370:tid 140609184798848] AH00046: child process 29443 still did not exit, sending a SIGKILL
[Thu Jun 28 21:05:46.440134 2018] [core:error] [pid 29370:tid 140609184798848] AH00046: child process 29444 still did not exit, sending a SIGKILL
[Thu Jun 28 21:05:46.440199 2018] [core:error] [pid 29370:tid 140609184798848] AH00046: child process 29446 still did not exit, sending a SIGKILL
[Thu Jun 28 21:05:46.440260 2018] [core:error] [pid 29370:tid 140609184798848] AH00046: child process 30150 still did not exit, sending a SIGKILL

 

[elderbre]

*Recurring, not concurrent...