Man, I lived that same nightmare scenario with the flipped G-S pins on a MOSFET. I had the board spun and excitedly soldered it all up. It was a relay logic pr

Man, I lived that same nightmare scenario with the flipped G-S pins on a MOSFET. I had the board spun and excitedly soldered it all up. It was a relay logic project with a few micros, tons of LEDs, swaths of general logic chips, and a lot of relays. It was a hybrid mechanical computer, nothing massive, but a lot of components. Fired it up for the first time and got nothing. Just like OP I narrowed it down to the relay coils not firing. No signal out of the driving MOSFETs. Being a fool I had trusted a random online library for the MOSFET footprint, and of course the footprint had the G-S pins flipped. I painfully bodged one before deciding to just bite the bullet and spin another one. I cannot imagine doing 300 like OP did, good on him.