Secondary panel in garage, fed by 50 amp circuit from main.

Panel is acutally a main service panel, but used as a sub, brand is Eaton Cutler-hammer

Anyway, yesterday morning garage door doesn't open, inside garage the fridge is off and warm(lost all of my boar meat).
They are on different circuits, but I did not know that. I blamed the gfci receptacle that protects the other receptacles on the lower floor, took it out and just connected the wires in a wire nut, still no power.
Trace the line with my voltage tester, no power all the way back to panel.
Turns out such is the case with three circuits.
Killed all circuits but one at a time, no power confirmed. Changed the breaker in each circuit, still no power.
Moved location of each breaker in the panel to unoccupied spot, each gains power. Tested switching circuits in each spot where another did not work, no power.
There is no crack in the bus bar or visible damage and very little power is drawn in the garage, the fridge is always on but otherwise just occasional lights and the garage door 4x to 6x per day.

So what on earth could cause certain spots on a panel to just not carry power?
I plan to test each spot with a length of wire and a light this weekend, I just wanted to hold of tweaking the wiring in the garage until later because it is more or less wired correctly.