ok so a little more info here: the segfault occurs *directly* after a logrotate-inspired signal is received.
[Sat Aug 19 06:25:37.746265 2017] [mpm_event:notice] [pid 21345:tid 3074504512] AH00493: SIGUSR1 received. Doing graceful restart [Sat Aug 19 06:25:39.647852 2017] [core:notice] [pid 21345] AH00060: seg fault or similar nasty error detected in the parent process an attempt to get more information by using mod_pagespeed's crash handler *failed*. one of the developers mentioned that there's an option to get stack trace output put into the error logs, but bizarrely (no explanation yet) we got.... absolutely no output when the segfault occurred: just the standard apache2 AH00060 notice. this is all very strange.... and i can't keep risking a live-running client's system by using unstable software. so, apologies, i'm going to have to return to using mpm_prefork (i.e. can't risk doing further tests with mpm_event on the live system). performance was *significantly* degraded around the time of the segfault.
