Why did my ECU fry?

So, I've been running a flash ecu on corn for the last few years. Car had been down for 2/3 of this last year undergoing some upgrades. Go out to start it in winter in storage and let it idle up to operating temp. After about 10-15 minutes of idling, car just dies.
Start it up again, let idle, after 10-15 it dies again.
No longer can get it started.

(Im going to lay this out in an event chronology to make it easy to follow my thought/action process)

Suspected fuel pump, take cover off - wiring to pump is FRIED - I have a hotwire from the bat to the pump hat direct using the ecu trigger to kick on the relay. - specifically the power wire from the relay to the pump hat had gotten hot enough to seperate a 10ga wire.

Ok, so a surge appears to have happened out of the blue.

So I repair the wire. Put it together. Car starts. Runs fine for 10-15 and does the same thing again

- think that the pump is going bad and has some sort of short, pull cover off, wiring looks fine.

Pull pump from tank - apply battery voltage, pump whirs to life

Then go to crank and hear buzz from dash - the mfi relay!

Order a new one from cherry hill, swap still buzzing and no dice.

Swap my flash ecu and harness for my stock tt ecu, look to crank the car enough to get it to pop on for a very little bit, not run (stock ecu wont drive 1250cc injectors).

Car cranks, but no pop on, but the mfi relay no longer buzzes, confirming the flash ecu met it's end.

So now this leads me to here - may have an oppurtunity to swap in an aem to get this thing online, but what in our cars would cause an electrical surge to make the ECU fry? Or for that matter prevent starting?

Would a bad ptu/coilpack setup kill a brainbox? Short in the harness?

Pull the fuel pump hanger again.

Confirm the power wire (think it's the blue wire) isn't making contact with any part of the hanger except the pump.

The aem actually has less shielding than a stock ecu, so I would definitely figure this out before considering a swap.

Sounds like a transistor may have just burned up on the ecu, that circuit is pretty simple.
Probably easy fix.
Just wondering what relay were you running for all those years?
Or is this hot wire a new upgrade?
Is this one of my ecus?