i a similar problem it was cause (well i think) the reset line on the trap door was dirty and if i reset it it would not boot but if i powered down and left it off a wile it worked if i removed the card and pluged it in it booted up fine.
maybe the heat caused the board or socket to flex and loose connection.
when the board was cold it worked normally but not when it was hot
when i cleaned the trap door socket and pcb it worked great from then on
