Welcome to here.
Because of the mc4000 not being a smart console, only a midi controller, any performance issues are going to be resolved by changing something like a setting in the laptop or VDJ.
I can only guess what you mean by stocking as it’s only a term I’ve heard for something I like pulling off girls legs . But I would guess you mean that after 30 seconds of the music playing ok, the music starts playing with stuttering or chopping noises or sounding like as underwater. The cpu loading figure can mislead, like VDJ wouldn’t want you to think it’s working your laptop too hard. I’ve seen video processor /editor packages give false cpu load readings. But knowing the rest of your laptop specifications would be good like RAM also what else might be running and you’ll need to optimise your laptop.
Did the same combination of that laptop, that VDJ version and that controller work well for months but recently has given this fault or has it never worked perfectly? Does this bad happen straight away or only when the laptop has been running for a while ?