Guys my w212 (E200 year model 2016, engine gasoline 2L, automatic transmission 7 gears) has a problem. Every now and then at almost certain speed of 20 km/hour, the RPM during acceleration at 1.5 goes back to 1.3 then continues normally (please see uploaded video). After 30km the car is normal. The acceleration and power in general are normal. Only at this speed the RPM hesitates and you can feel it while driving (sometimes light and sometimes heavy). I got it checked at the dealer and no engine or transmission faults are recorded. There were suspensions to a faulty torque converter. The dealer proposed an adaptation to the clutch lock-up (they call it learning). When the went for a test drive with a scanner connected, they noted that the lock-up clutch readings are excellent so left it without adaptation. By the way, the car 12 V (80 Amp) suffers some weakness. Could this cause the problem as it may provide insufficient electricity to the systems causing the problem?

The issue happens at E or S modes, irrespective of the motor's temperature, but i noted that after some while in driving, the problem goes away.

The car has done 20,000 km so very low mileage.
Any thoughts are appreciated! Thanks guys