why my virus in Hypersaw the notes tend to sound fatter or thinner at times

Didn't listen to it yet, but any sound that uses detuning, cancels out frequencies at times. In order to make this phenomenon less conspicuous, spread out the detuned waves a little further apart from each other, so that the cancellations will turn shorter and more frequent, becoming a part of the timbre, and not isolated events of thinning out.