Sorry for responding so late but it has been very busy here lately, so I haven't checked new Discourse post for a few days. I have also seen your reply in
https://github.com/pi-hole/FTL/issues/198
and I guess you are right. However, there is one strange thing with your backtrace, that is
#5 0x00445664 in getClientsOverTime (sock=) at request.c:1155
where there is no value given for sock.
Have you tried the possible solution I posted in the issue mentioned above?
I deployed a fix for a likely cause of this issue, but as we are already preparing for FTL v3.0, the current development version won't work for you. I prepared a backported fix, you can try it with
sudo pihole checkout ftl master-fix/ssend