2017 Jetta S 1.4T misfire - P0141, P0303, P0304

This morning I was commuting to work in the New Hampshire snow, ~17°F. About 40 mins into my 55 min commute (mostly interstate), I was accelerating on an on-ramp, and my CEL started flashing, and I got a steady EPC light. The car started running pretty rough, driving in 4th felt ok at 70 mph, but if I put it into 5th it got rough again. Probably should have pulled over sooner, but 10 miles down the road I got to my exit, and at a red light I restarted the car. Everything seemed normal. Lights disappeared, engine felt smooth again.

When I got to work I plugged in my OBD reader, I had 2 pending codes...

1. P0141 - "Oxygen (Lambda) Sensor B1 S2. Heating Circuit Malfunction"
2. P0304 - "Cylinder 4 Misfire Detected"

After work I wanted to swap my spark plugs and coils around to see if it was a problem with those causing the o2 sensor to malfunction somehow... but I JUST took my spark plug out of my car... It seemed to be driving fine, so I just cleared the codes and started driving.

25 mins into my drive I stepped on the gas pretty good to close a gap between me and the car in front of me in traffic... CEL flashes a few times, light goes back to off but I plug in the OBD anyways. Now I had:

1. P0303 - "Cylinder 3 Misfire Detected"

But no oxygen sensor code...

On my INNOVA 5210 OBD reader I left plugged in while driving, my "O2S B1 S2" value varied from 0.0 to 0.810 (V) depending on my throttle input.... my "STFT B1 S2" value stays pegged at 99.2 (%) no matter what I do. Is this the problem? Do I just need to replace my downstream O2 sensor?

Is it possible my O2 sensor is just frozen? Over the last 2 weeks, the highest temperature we've seen is 35, lowest is -9, average is 14. I don't have a heated garage, but I could leave my car in one for a few hours while at work if that might help.

All 4 coil packs and spark plugs are only 8-9 months old, all replaced in May 2025. I just replaced my original battery the car shipped with 2 days ago, maybe that somehow made a difference?... I put in a "SLI47H5M Duracell Ultra, Group 47, 650CCA, Gold Flooded" battery as recommended by the battery store's website.

My mechanic friend suggests I just replace the o2 sensor... Just wanted a second opinion, he hasn't been a mechanic super long and doesn't work on a ton of VAGs.

Any ideas?