Calibrated several times, it is much faster now! 5min...
The synth is very much more stable and no supprices when playing.
Lets see What happen in close future
I had a period too, where a few calibrations was needed until it finally was rock solid, so I do not think you have to worry anymore.
You can also enter diagnosticks mode (I cannot remember the button combination to enter though) and perform a "clear calibration data" function prior to calibrating, if it starts to act up again.