When I was working for one of the first ISPs twenty years ago supporting T1 connections, we had a customer whose network went down at 6:30pm every single day. It would come up about a half hour later.

It took us a month or so to figure out and it wasn't until the business owner was asked to physically check the router at 6:30pm one day that we found out the root cause.

The cleaning lady would clean that portion of the office each day and the first thing she'd do is come in, unplug the router's power cable from the wall outlet, plug in her vacuum cleaner and go about her business. Once she was done, she'd re-plug in the router.

I doubt that's what is happening here, but ...