My GNX1 doing some strange things...

Lately I am getting the following problem: while I am playing something the level suddenly drops a lot, even goes silent. Then what I have to do is unplug the cable that goes into my guitar and plug it again and it goes back to normal level. It also gets fixed when I strum really hard the strings.
So whats the problem with this thing, I have this unit for more than a year and half and it has not done anything similar?
Could there be some problems with the cables I am using? They seem to work just fine when I am using them without the gnx1.
Any feedback will be appreciated.

Over the internet, all I can do is guess, but I think the problem is either the cable, or the jack on the guitar.

Ok I'll have them replaced and see what happens then.
Thanks anyway