Whenever my wife or I start a torrent on her Windows PC (wired), my Windows PC (wired) or my Ubuntu Laptop (wireless), our entire network loses connection for 5-10 seconds.
I have tested this with extremely small and extremely large files and after the 10 seconds or so are over there is no further issue, even if the torrent is still going, or even if it finishes in 1 second. I've tried limiting the max bandwidth on the torrent clients to as low as 500kbps. It does not seem to be a bandwidth issue.
We are using a Netgear R6350 Router connected to an Arris Surfboard SB6183 modem on a 500/50Mbps DOCSIS 3.0 connection with Xfinity/Comcast.