Bad sound with Gain maxed. Roll it back a bit - fine

[Tremster]

(I wanted to post this in Tech Help, but since it doesn't concern any Madbean projects I'm posting it here. I hope that's ok)

I hadn't built any pedal in about two years but recently the bug bit me again and I built some fuzzes. And unlike before they all work.

I have a weird issue with these two, though. Clones of the Analogman Astrotone and the KMA Fuzzly Bear, both built on Fuzzdog PCBs:
https://shop.pedalparts.co.uk/AstroTone_Fuzz_-_Sam_Ash_Fuzzz_Box/p847124_8861948.aspx
https://shop.pedalparts.co.uk/Ursa_Fuzz/p847124_19816586.aspx
BOMs are on these sites.

When I crank the gain they both sound weird, the sound cuts out, farts and splutters. Roll back the gain just a tad and they both sound fine. It's just that last millimetre on the gain pot.

The power capacitor on both these pedals is 47uF. I upped it to 100 on both but with no effect.
I checked all the values I used and they are correct. I reflowed all solder joints.
What else could I do? Any ideas of what this could be?

(That KMA Fuzzly Bear is one amazing Fuzz btw)

Thank you!