@Carl Different buildings but part of the same circuit breaker, so it shouldn't be an issue, other than wire distance.

@Carl Looks like the units are too far apart to work correctly somehow. When i plugged all 4 of them in the same building, they all work flawlessly without the issues mention above. Looks like i'll...

So i have a setup of 4 powerline devices, all of them being PA4010P. Lets name them P1 through P4 for easier illustration of the issue. P2, P3 and P4 are the closest together in terms of wiring...