Well Tuukkuli, unfortunately, based on your response, I'd say you've covered all your bases in eliminating outside factors from being the cause of your issue. While I am not experiencing this, and many people are very happy with the ones they have, you certainly sound like you got one of the few that may be defective. One concern that I have is that you mentioned it the second gimbal. If both are behaving the same way, and the behavior is pretty extreme from your description, it leads me to suspect that it may in fact not be the gimbal at all. The "odds" of you getting two defective with exactly the same issue is pretty low. I would seriously consider the flight controller since the IMU of the WKM determines and is greatly tied to the gimbal performance. The IMU V2 may certainly make a difference, and if it does, I would certainly like to know. Its very possible that DJI optimized this gimbal for the A2, but that is speculation. It is however a major difference between your setup and mine. When I had my WKM, the upgrade to the IMU V2 was subtle, but the switch from GPS to atti still included a change in prop speed, and a drop in altitude. While the WKM claims you can freely connect devices to Canbus ports, the A2 is extremely specific in what can be connected where. The main controller of the A2 clearly is more capable, as the issues I experienced with the WKM are gone. I don't know where you are currently located, but would be willing to pair your gimbal with my A2 for a real world test if you want. Im in CT. If thats not an option, I would encourage you to submit a video of the copter/ gimbal exhibiting the behavior, show them that its way beyond "firmware" and escalate support through your dealer and DJI.
Joe