A couple of months ago, my selector switch broke (the knob on it) so i got it repaired at a music shop. As it snapped off, they replaced the whole switch I've noticed that sometimes when im playing, the volume kind of cuts a bit, as if its reduced and the high pitch squealing you get with feedback sounds. I have to move the selector switch up and down a few times to stop this from happening and for it to go back to normal. As i play in a band, this is really annoying and can't go on. Is it the selector switch they fitted?

it never did it before they fixed it. Thanks
maybe its a cold solder joint so just get them to re-check to see its that or maybe a wire coming loose