I don't see periodic packet loss as a very convincing indicator of compromise by itself. It's more likely a shared part of your ISP network, beyond your front

I don't see periodic packet loss as a very convincing indicator of compromise by itself. It's more likely a shared part of your ISP network, beyond your front door, overloaded or struggling. In your router you should be able to monitor things like link snr and see how it acts when working well and showing the problem. Same with packetloss to your gateway.