Yes, and many kinds of plug-strips. These often have so-called surge suppressors that tend to attenuate high frequencies - and that can attenuate back into the wall outlet. Some new TV/cable boxes have surge suppressors. Some light dimmers rooms away can interfere.My experience with GFI breakers has not shown throughput loss.
What will really kill throughput are "wall-wart" type power supplies, cellphone chargers, etc. I always unplug all those in the same and next room when testing in one of my locations.
I found that connecting power line IP devices to an outlet with no other such things usually works OK.