Ok could be noise,distance or phase issues
For the noise find out what else is on that circit radio/tv/micro wave
I've read where you can use a portable fm radio tuned to a blank station moving it close to different out lets where it picks up increased static you have a noise problem ( I've never actually tried this!) you can also just unplug the devices which are on the same circit just turning off wont work. Once you find the problem device a filter can be purchased to eliminate the noise. Distance problems are mostly RF problem but in a large home long runs of wire can cause a problem as well especially if both the CM15a and the problem Module are at ends of different runs. Amplifiers can be purchased if this is the case.
Phase issues is the number one problem most users experience and you've already tried the test without any confirmation but if it is of any help that test didn't help me either. so here is another move your CM15A to the same circit as the floods and see if that helps it won't tell you for sure if it is a phase issue as it may be distance but if it still wont work chances are it is noise as it should work on the same circit.