fuzz face squeals at high fuzz level

I just finished building a silicon fuzz face with BC108s. When I turn the fuzz all the way up, it squeals like crazy. I have to back off the fuzz a bit and it goes away - like just tiny turn.

Is this normal for a fuzz face or do I have a problem somewhere?

I am building the negative ground version. I have installed the electrolytic caps "backwards" for negative ground.

I am using a Cioks power supply that's outputting just over 9 V. I have also tried using a battery with voltage just over 9 V as well. I re-bias every time when switch power options.

I am plugging my guitar into the FF and then into my amp - no other pedals or anything.

I have biased my Q2 to 4.5 V

I am using a pcb I got from tayda.

https://www.taydakits.com/instructions/fuzz-face/pages/designators-and-components--26

I've noticed something odd while messing around... when I put my finger across both transistors (top of the can), the squeal completely goes away. It was suggested to me on FB that I try putting a 47 pF cap across Q2 base and collector. I don't happen to have a 47 pF on hand but I do have a 68 pF. I tacked the cap into place for testing. It made no difference adding that cap.
I also tried soldering the same capacitor to the tops of the transistor cans like a bridge (like what my finger was doing). Then I tried using a jumper wire to do the same thing connecting the tops of the transistors. That also made zero difference.

The only thing I changed from the instructions was to use a 1KC for fuzz pot instead of 1KB