Sounds like a case of the wrong switch. I've come across similar before.
A depot I used to support had a small portacabin as the office. This cabin had one desk with a computer, a phone and a printer plus the overhead light. That was the extent of the electrickery in the "office". There was just enough room in there for a the desk and chair and a small comfy chair for visitors.
So one day we got a ticket that the PC was very slow to respond. Service desk asked what they meant by "slow to respond" the site manager said it took ages to open email. The only application he used most of the time. The RJ45 connected to the main depot building in which was an aging Cisco 1700 series router with a pitifully slow ADSL connection. Quite why the router was in the main building and the PC outside in a cabin I know not, but that's how it was set up. Anyway the connection was so slow that remote controlling the PC to investigate simply wasn't an option.
So I traipsed out to site. The manager was sitting at the desk when I arrived. I asked him to close and re-open the email app which it did pretty quickly. He opened an exiting email without issue. I sent him an email from my phone and there was no real problem there even given his very slow connection. So I asked if this was a continuous problem or intermittent. He explained that the specific issue was that he spent a lot of time out in the depot, but each time he came back to the office it would take an age to open his email app to check his emails. I asked why he was closing the application every time he left the office. Could he not just lock his PC? He denied that he was closing the application.
I was racking my brains to wonder what he was doing. Could he be opening a new instance of the application every time he came back to the office? Maybe the rather crappy old PC was simply running out of memory. So I decided to get him to show me the issue. I suggested we go for a walk and then he could demonstrate. So he stood up and hit the "light" switch. Off went the light and I could hear the PC fans spinning down under the desk.
I looked at the switch. It wasn't a light switch, but a fused spur switch, half way down some trunking that ran from the double socket by the desk to the ceiling. More trunking ran across the ceiling to the light. And further trunking ran along the top of the wall at ceiling level to the corner behind the door. From there more trunking ran down the wall and disappeared behind a coat on a hook. That switch was cutting the power to everything in the cabin. I checked outside and sure enough overhead power, ethernet and phone cable ran the few feet from the main building to the corner where the trunking terminated. The power ran down to that switch. The power also rain to the light fitting and then in traditional style a cable ran from the fitting back through the trunking to a switch hidden behind the coat and a hi-viz jacket. The coat was the manager's the hi-viz had been there since the day he began work at the site and he'd never thought to move it.
He had genuinely never noticed the light switch and was using that fused spur switch to turn the lights on and off.
Quite why that fused spur switch had been installed at light switch height I don't know. But his predecessor had managed to set up the PC to auto logon. What he saw as it taking ages to open email was the PC booting up and logging in and then him opening the email app.
We'd have noticed the issue much sooner if the router had been sited in the logical place rather than on a little shelf in the depot toilet (yes really). We monitored all the routers with SNMP, so had the router been in the office we'd have seen it powering down several times a day.
So I got onto facilities and had the cabin wired properly with it's own little dis board. As a courtesy I also got the bloke a decent up to date PC as the one he had looked about ten years old. Unfortunately there was not much I could do about the DSL connection on a line that was about 7km long.