I think this is NOT an individual problem, but a fundamental technical bug within the producing-process of the controllers.
The problem with the uneven pads was discussed a long time ago and the solution was: Send it back to your dealer and get a new unit !!! This is the only solution, because ALL spark-units of the "first generation" have this problem with the pads loosing the contact to the platine.
ALL pads become uneven with the time, the pads of the step-sequencer, the pads of the cycle, the main trigger-pads etc.
After sending back my first controller ("first generation") and get a new ("second generation") there are no problems any more with uneven pads. But it takes 4 (!!!) weeks to get a new one
The words "first generation" and "second generation" are not "arturia-official", but it means: the first set of produced spark-controllers and the new (better) produced units. Even if you bought a spark some days ago, you maybe have catched a "first generation" unit with the known problems of the pads.
Sorry for my English.