[rmetzler]

I also found a test breaking on Mondays. Never on any other day. It tested a sum for the current week but made the mistake of creating models for "yesterday" which is on another week if it's the first day of the week (depending on location, Monday in Europe, Sunday in the USA).

[martinpw]

Had an office where, every Thursday, one developer's machine would reboot at the same time late in the evening. It didn't happen to anyone else. Eventually he decided to stay late one Thursday and watch it to see what happened.

At the appointed time the cleaner came by, unplugged his machine from the power socket and plugged in the vacuum cleaner to clean the room, and when done, plugged the machine back in.

[staikken]

Heard a similar story about a laboratory system with tight environmental controls. Every so often the humidity would spike and the room would go out of tolerance after typical work hours. The designers of the system were under quite a bit of pressure until someone finally stuck around long enough to catch the janitor mopping the floors.

[dvtv75]

Some decades ago, friends of mine ran an ISP that resold bandwidth from another business. They used a leased line to the business, and every Friday evening at about 7.30 their connection dropped out.

It turned out that the cleaners at the remote end would plug their vacuum cleaner into the same circuit that was powering my friends' hardware. The power surge caused their hardware to crash, and nobody had access to properly reboot it until Monday 8.30am.