Hi, I would use output processor's pin "Reset USB" as an external output, this is very useful for me to open a door remotely, as I can manage it by script in many different ways.

The RB750r2 has the same PCB of RB750UPr2, where the USB is sold and operative, I suppose the U600 is the USB's power supply, and I bet it has the enable pin connected to the main processor for power off the USB and reset the LTE when needed, but I can't find it.
Looking the pictures I've measured all the U600 pins and the places for resistors around it (red marked), at normal router condition and when USB power reset (I put 60 seconds) is active, I always measure 0, so maybe there is another resistor on the PCB missing, not close there. Any ideas?

Can you write here the U600 name? Can't read it from the photos I can find, it may help, thanks!

I think I found it, LSP5523, the pin 7 is the enable, it should be high to make it work, but I don't have voltage there, there may be two reasons, the FW knows ther eboard doesn't support USB and disable it permanently or there is a jumper or a missing resistor (probably) somewhere else

Found it! Works with USB reset command, there is a micro jumper, hard to see with human eyes (at least mine! ) it's necessary to joint it to have a better place to solder at pin 7 pad. It switches from 3.33v to 0