Minitaur LFO Rate problem?

I have recently bought a Minitaur but I am experiencing problems with the LFO rate. It doesn’t matter if I use the unit with the Standalone Editor or without having it hooked up to my laptop.

Basically when I turn up the LFO rate to the desired setting and start playing on my midi keyboard using mod wheel to control the LFO everything works fine in the first minute or so. But after a few minutes the rate slows down automatically and then I need to readjust the setting.

Readjusting is not a straightforward operation either: first I need to reset the knob by turning it up and down completely. After that I can start to reset the LFO amount, but often when I get close to the desired value and slown down/ stop turning the knob to have a close listen and then want to turn up or turn down the LFO amount a bit again the LFO Amount gets stuck in the last value that I was listening to. Then I have to reset again by turning the knob all the way up and down again.

Am I doing something wrong? Or is it the knob itself that is defected? Any tips are welcome!