It's possible the injector is not atomizing as it should.
During cold starts the engine runs pig rich and ecm adjusts timing accordingly to provide a fast warm up however upon operating temp injector duty cycle is dialed back for smoother idling as the timing goes down to 10 degrees.
An injector that's not atomizing properly will dump droplets instead of fine mist causing a misfire.
This happening on cyl one can confirm the theory a bit since its the first cyl that receives fuel. Whatever contaminants passed the filter hit the first cyl and possibly changed the spray pattern.
You should look into having them cleaned and flowed first before you keep going down the diagnostic road.
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