"disc not ejected properly" - on a networked Time Machine backup

Hi, on one of my Mac (13" MacBook Pro M1), ever since upgrading to Ventura I get frequent errors of "disc not ejected properly" for my Time Machine backup. Which is stored over the network, and the network server (a Synology DS950+) is not having any availability problems. Usually network shares don't give the "disc not ejected properly" error even if the server they're on goes down, anyway -- they would normally say "the connection to the server is interrupted."

Why has macOS suddenly decided that my networked backup is a physical drive that's disconnecting, and how can I get it to stop?

I've tried disabling and reenabling Time Machine, but that hasn't helped.

Sometimes I wake up my Macbook and have around a dozen of these notifications popped up and they have to be dismissed individually. It's quite frustrating.