OK so I've had this issue for roughly 6 months now and with my Google detective work I've been unable to find a solution.
Whenever I open the Desktop app on my PC the Ethernet connection is completely cut off and so I'm unable to use Spotify. I've reinstalled the app may times over the 6 month period hoping a patch may have fixed it but I'm still without any luck. I have two other devices in the house that work fine over Wi-Fi. One being a laptop (using the exact same app) and a Smartphone.
Spotify is definitely the reason my Connection is cutting off. It is the only piece of Software that has ever caused this problem.
I'm sure I can't be the only person out there with this issue so I'm looking forward to a response.