Fuzz guitar pedal - not so fuzzy anymore

Hello.

Me and my son made the Fuzz guitar pedal from the Velleman kit (K8113) It worked very well and the boy was very happy with his first pedal.

Few weeks later it lost it’s fuzz effect, now it just sounds like a blown speaker.

First we thought the battery had ran out but we changed for new one but nothing changed.

Any idea of what have happen?

Sincerely
Siggi

I would look at all of the solder points.
Maybe one came looses
Just a guess