I've been trying out tethering apps to try to find one that works. After failing with several of them, I came to JB WiFi Tether. It also didn't work (simply prompted me to choose a tethering plan). I had read a review that suggested it might work after rebooting. It did not.
Now, I've uninstalled it, but my phone reboots itself roughly 90-120 seconds after booting, every time. I've wiped dalvik and cache in TWRP, to no effect.
What next? I'm not opposed to doing a factory reset if that will fix it.