Temperature is a bit colder now, maybe your cold start settings need work. See how much fuel is being added when engine is cold, and see as ECT increases if this added fuel tapers off.
Normally when an oxygen sensor is on the way out I've seen them either go really erratic on AFR, or they tend to stick really rich or lean and can throw you off.
If you have a closed loop AFR system enabled, check to see if its fighting to either add or remove fuel as it's constantly out of range
With engine off and ignition on, use Syvecs to test output to each injector. Can you hear each solenoid click?
Do a quick test whilst car is idling, choose the cells that are being used and take -15% fuel out. If your AFR dosen't change then you know you probably have a sensor issue.