I have a pair of powerline ethernet boxes set up to connect the top floor of my house to the rest of the home network.
Periodically, I've found that the network in the rest of the house becomes extremely slow. Disconnecting the ethernet from the powerline ethernet appears to fix the problem.
I originally thought it was a problem with the powerline ethernet boxes, and replaced them with new boxes. However, the problem has reoccurred with the new boxes, which makes me think that it's not the boxes, but something else.
Unfortunately, I don't know what that would be.
My home network is rather complicated, with several switches. Yet the networking disruption appears to occur across the entire network.