PLC is first line?

[K4680]

But I wondering why my PLC performance is so terrible? Wish I had decent PLC connection between the rooms.

Hi, try the devices (PLC) directly wall socket. If you operate the PLC via power strips, the throughput drops rapidly, as it is with line filters or isolation transformers !!

5 of the Phantoms are hard-wired through the wall and mounted with Gecko. The remaining Phantoms are connected to sockets, but they are on 3 different circuits. The same circuit as the Dialog is the one performing the best. I think its the back and forth between Wifi and PLC that really is causing most of the issue. 

I looked up line filter and isolation transformer, what are some common products these are in? I have not installed anything like this myself, but is it possible that the electricity company installed something like when the apartment was built?

Hi, no, this is not installed! For example, filter socket strips (Isotek, Supra etc) are meant! It is true, they are different circuits, but always the same phase!
On which fuses (Nr) are the phantoms connected?

Another problem with the PLC is fault protection (FI), which disturb the transmission in the high frequency range. And that is your problem! With you combi fuses are installed (ABB DS202CM), FI switch and fuse in one unit!