When I first started building stuff on vero board in 2019 or 2020, I picked a Devi Ever fuzz because it seemed pretty simple due to the low parts count. I did everything meticulously and then it didn't work. My LED lit up when the I hit the stomp switch, but I had no audio unless it was bypassed. I reflowed every solder connection, double checked the cuts, made sure I didn't bridge any traces, the whole nine yards. I was ready to hurl the thing into the wall or the trash, I couldn't decide which. Somehow I figured out that I was orientating my stomp switch 90 degrees sideways compared to the way the wiring diagram showed. Of course this diagram didn't show which was the pins on the switch were running so I had no way of knowing until I noticed someone else's vero build had the switch turned.
One of the big muffs I built last year (maybe the Hoof clone) worked when I finished, but the volume output wasn't even unity when maxed out. Turned out that the collector resistor in q4 (supposed to be 10k) got a 1k in it's place. Once I swapped it out everything was copacetic.
The thing I've learned in my case is that it's almost always something simple, but once I'm irritated things don't stand out as easily lol. I take a break, sometimes don't even mess with it for a day or more. Hell, I had a bluesbreaker clone that sat in the drawer for six months because I fucked up the tone pot cramming it into the enclosure. That's how I learned to solder the components on the board, screw the pots into the enclosure, then lay the board onto the pot legs to solder that stuff waaaay more easily. It's so obvious now, but someone it didn't even occur to me.