There should be no need to restart after enabling core per pid.
Can you see the next log messages after:
``` Aug 7 22:44:11 ip-172-31-46-236 /usr/local/sbin/kamailio[9477]: CRITICAL: <core> [pass_fd.c:277]: receive_fd(): EOF on 30 ``` This is just saying that one process stopped, but not the reason why (signal, etc...), the log messages after it provide some information.
You can also try to run with latest branch 4.4 (pull, recompile and reinstall), I just backported a patch that should take care of handling the exit of additional processes created by libs, respectively:
* https://github.com/kamailio/kamailio/commit/78684f2bba3d408e60eb8450bf915ebe...