"We had a "computer room" (old office on the top floor, south facing, floor to ceiling windows and no AC).
In 1970 we had a network of comms nodes round the UK based on M2140 industrial computers. The one in Manchester would randomly go down in the daytime - and then come back before the engineer arrived.
One day the root cause was finally identified.
It was housed in a small room with large windows. The cabinet doors were often left open after scheduled maintenance. If the sun shone long enough at a particular time then it illuminated an exposed rack of cards. There was one faulty small IC that distorted slightly in the extra heat - breaking one of its pin contacts inside the package. When it cooled - the contact was re-established ok.