PyBoot.py stops at Exploiting device with checkm8

[beeaniebee]

I used Divisé to install iOS 12.4.1 on my iPhone 6s and when trying to boot, I select the right model, n71map, then again, and it pwns the device the first time just fine. but then after the Signing boot files it says Exploiting device with checkm8 and just stops. I know I rebooted the device fine and it went into DFU mode ok, verified with irecovery -m but then it just stops. Manually terminating the program with a keyboard interrupt shows that it stops at line 283 at so = os.popen(cmd).read() every time. Any help? I'll try a different usb cable, and if that doesn't work, an old Mac on an old version of macOS, just to see.