My best guess, again, is very likely a power problem. Can you give more info about how Teensy 3.6 is getting power? Is is plugged directly into a PC? Or into a hub? Is that hub powered or unpowered (getting power only on its USB cable to the PC)?
Maybe try using a voltmeter to check the VIN pin, to see how much voltage Teensy 3.6 is receiving. Also (very carefully) check the 5V output on the host port, to see how much voltage Teensy is giving to your hub to run. My guess is these will probably show voltages much less than 5 volts.
Ok, so here's what I found out:
Teensy 3.6 getting power directly via USB from Macbook; nothing else connected to Teensy.
-> VIN pin on Teensy: 5.18 V
-> 5V Pin on host port: 4.85 V