Anything else that could cause both upstream o2 sensors to suddenly throw codes for no activity? Seems weird theyd both go out at the same time

You will need a multimeter. See: https://www.alldatadiy.com/techtips/ALL ... 91031.html
and test. Get some sandpaper too. For the extra ground, I just used 10 gauge wiring from Lowes and made 2 harnesses to attach to the battery negative.

according to that TSB, this doesnt apply to mdel year 2001 pathfinders or qx4. only up till 2000. that said....i tried this anyways, although the grounding point arent in the same spot...and it didnt help anything

Yeah I know that the TSB "doesn't apply" to your model year, but whenever you get a no activity issue for front O2, it's because they're either defective or are not receiving the required current, either due to a grounding fault (gotta test voltage drop) or a PCM issue (gotta check if the PCM is properly giving required voltage.) You're using the service manual? Steps are usually outlined under engine control system (EL).

Outside of chasing a short/grounding fault, perhaps buy one of the cheap O2 sensors and use it to see if you can get the fault codes to follow?
It's not ideal, but outside of poor grounding or a short, I'm not sure where the issue could be.

Both suddenly failing does sound odd. And no fun to change, especially the passengers side. They're due at 100K, although they rarely completely fail, just not up to spec. But anyway, back to yours, while the sensor is a pain to get to, the plug isn't too bad, find the signal wire and check for voltage. That should give you some direction.