When I worked for a paper mill we had a machine lose memory, lightning storm I think. The Allen Bradley PLC had an EEPROM backup so we uploaded the program from it.

Counterintuitively to the maintenance section, "upload" to A-B means upload FROM the PLC, not TO the PLC. So we loaded the empty program into the EPROM, erasing it.

Not a problem, we had another EEPROM safely locked in a cabinet in the office.

Of course we repeated the same mistake on our only backup.