This hasn't happened previously (for me), so maybe an update is causing this to happen, but-
When I open Spotify on my phone it wakes my computer (sometimes I think it does this even when they're not necessarily connected to the same network). This happens on both computers I have on Windows 10, I feel like maybe the problem is that it has a popup on the computer lockscreens that shows what's currently playing in Spotify. I'm not really sure, but has anyone had this issue recently?
I know it's about 2 years later, but I can confirm I'm having the same exact issue. I've isolated it down to spotify, since putting my computer to sleep, it stays asleep until the instant that I open spotify on my phone, then my computer wakes from sleep. It's a bit of a nuisance since this isn't something I have any control over. I know that I can disable the ability for magic packets to wake my computer, but I have that enabled for other software that I would like to keep that functionality for. I'm pretty sure that it's related to how spotify connect works.
As a quick update, I found that one way to avoid this (at least with Spotify for iOS) is to go to the Spotify Settings > Devices and disable "Devices on Lock Screen", as well as disabling Background App Refresh.
I'm not sure that I needed to do both of these, but the combination of these two things also reduces the ridiculous battery drain of Spotify on iOS (specifically on my iPhone 7)