Reply to Synth help!!

Hey guys, so I'm producing my first deep house track and I'm constructing my chordsss with VST Polysix.


My question is, without fiddling with any of the parameters, the cut off frequency on the keys change from low to high, why?

For example, if I keep on pressing C3, the cut off frequency will gradually increase then suddenly drop and start again. I can't get a consistent rhythm without it ascending and descending, why is this?