The server goes down

I made an environment of umbrel with “Raspberry Pi 4” and “SSD 1T”.
Connected to the server in the room with a wired LAN, “Bitcoin Core” is still “Synchronized” and 40 percent.
Well, the server in the room goes down regularly.
Until now, this has never happened.
Is there a cause, a countermeasure (if it is due to “Raspberry Pi 4”), etc.?
Please let me know.

By the way, I am Japanese.
The server uses a product called “WSR-300HP” from “BUFFALO INC.”.
I look forward to working with you.

First, I made a mistake between the server and the router.
The correct answer was that the router went down.

The problem was solved when I replaced the router with a new one.
I apologize to you for a fuss over.