I don't have the time to go figure out what exactly is causing it, but if you build from source with the log4cpp dep missing after a merged PR in April/May(that fixed some log4cpp headers), then in certain circumstances, you will get a segfault, due to a heap buffer overflow.
There are a few code paths that crash. If gr-iqbal is installed, it will crash right on opening gqrx. If not it will crash when switching demod type.
I believe both cases a call to a destructor on at least 1 block, followed by some kind of printed message is the culprit.
Took me a few days to find the "fix", as I thought it was related to some new hardware I had, but then upon pulling I was able to reproduce on my normal workstation and it went away when I installed log4cpp and recompiled GR. Just though I'd throw this out Incase anyone else was having the issue.
I'll try to file a bug report, but ideally I would like to include more information and I don't have time for that atm, and from what I understand it might be OBE when 3.8 comes out as that's getting added as a required dependency.
I have not reproduced the crash in anything besides gqrx, but it seems pretty solid that it's a bug in GR. I bet other apps that reconfigure flowgraphs like shinysdr would trigger it as well.
-Don