The ECM doesn't really use the rear HO2S's for running the engine, they're only there to monitor the cats. So it's possible the rear sensor has been going bad for awhile but went unnoticed till the front one failed, which
is used for running the engine. I just checked the WD's and power/ground are common for all 4 sensors, and the data wires run straight to the ECM without intervening connections. That makes a wiring issue doubtful. I'd check power and ground anyway, but if they show up good then it looks like two bad sensors. See info starting on EC-133:
https://www.nicoclub.com/service-manual ... 7%2Fec.pdf