Interesting issue. I do recommend sending back to MTH.
I would also comment that video is a great source to get definitions insync.
When I first read your post I assumed it ran fine for 2 minutes or so and then developed a jerk that was consistent. In reality it runs fine, stops running correctly and than starts running fine which means it is not the Tach reader.
To me this looks like the motor loses power, and stops, followed by the processor thinking it needs to crank up the voltage to the motor to regain ordered speed and then takes off when motor power comes back.
Not sure if this has the FET or Relay boiler board, but I imagine MTH will change the boiler board out. Seems like a motor FET acting up.
I assume the 8 pin and 32 pin connector are fully seated in the boiler board? G
