My only unsolved networking mystery was that my computer would experience high packet loss when a Roku in the other room was streaming Netflix.

My PC and the roku device were both wired to two different ports on a router (iirc an Edgerouter X running openwrt at the time). This didn't repro when the roku streamed other services (hulu/youtube tested), only netflix. This also didn't repro if the roku was connected over wireless (connecting to an AP wired to a different port). Just opening netflix also didn't repro, the roku had to be actively streaming a netflix video.

I never ended up solving it, I just worked around it by making the roku connect over wireless.

It did take me forever to figure out the problem though. For a long time I'd be in one room getting frustrated with my computer while someone was innocently watching netflix in the other room.