Boatbod,
So I took the drastic step of starting over on one of my Macs running Linux Mint 19 by reformatting the partition and installing Ubuntu 18.04.1 LTS. After installing development tools and Gqrx, I performed the github clone. Made sure I was still seeing control channels from the Radio Reference pages via Gqrx and ran rx.py with various values of -q from -2 to +2. While trying to fine tune with '<', '>', ',' or '.', I did not experience any of the crashes that were seen the previous evening. I was able to center the waveform and sure enough, I received the NAC and the tsbk counters incremented along with seeing active talkgroups. I can now proceed to try and finish the installation.
On my other machine running Linux Mint, I will try just re-installing Gqrx and op25 as a control. Very strange that the installation would work on one and not the other. The Mint installations were identical except for the different drivers for the Mac variants (iMac vs. Mac Mini)
Btw, the same errors that 'Dseven' reported in the 'rpi3-rtl-sdr-op25' thread are the exact same crashes I see when either the tuning is way off or when the tuning approaches '0' on gnuplot. Not sure if you pushed any changes yesterday, but as of 10 PM PST, your op25 fork was working for me.
Thanks for your assistance in getting this going for me.
Chuck