The question here is what frequency is the noise source, and what is the filter tuned to reject. The AF120 is a notch filter. The schematic I have shows it uses 7.2uH inductors and .22uF capacitors. With those values, maximum attenuation is at 126KHz, which is a bit above the X10 frequency of 120KHz. Depending on component tolerances and how sharp that notch is, it is possible the attenuation may not be that effective at 120KHz. It is interesting that the Leviton 6287 is also tuned to the high side, but that filter has a larger value capacitor used as the leg of the "T". So, it will provide somewhat more attenuation to high frequency signals. The 5A X10 XPPF is a low-pass filter. While its maximum attenuation is not as much as a notch filter, it is more effective attenuating broadband noise
I installed fluorescent lights in our utility spaces. To avoid X10 problems, I chose lights with the older magnetic ballasts. I did install a couple of the newer suspended ceiling fluorescent fixtures with electronic ballasts in the rec room. While I haven't noticed any problem with X10 communication while they are on, noise from them does light up one bar on the ESM1. I suspect that noise is far enough away from 120KHz that the receiving modules are able to reject it.
Jeff