Hi Chris
Long time :
I guess you have Mod_LSAPI running in your server. Can you please confirm if that is the case.
If you have cloudlinux installed , then please check the below things
1. Check the site for any resource limit faults and especially memory related limits.
You can check the lve details using the below command
# lveinfo --by-fault ep
2. Another thing is if you are having mod_lsapi , please disable lsapi_terminate_backends_on_exit value in /etc/apache2/conf.d/lsapi.conf and restart Apache and check the issue again.
3. Another possiblity is mix installation of opcache like APC, Opcache etc . Please try disabling the opcaches completely
4. Also try increasing values like lsapi_backend_pgrp_max_idle, lsapi_backend_max_process_time to higher values .
Let me know chris whch ones works for you so that others can also get help from this at some point of time.