HLC/UPB Light Stops Responding to Off


Active Member
Recently I noticed a single light in our house was on most mornings after executing an "All Off" on the HAI.  I also noticed that it wasn't responding to the off command and the HAI thought it was off.
So, today I replaced it with a different UPB switch, reprogrammed it and.. same problem. 
The HAI turns it off maybe 10% of the time.  Oddly, it can reliably turn it on.  The scene switch that is used most often for that room never turns it off when turning off the room.  
Interesting, I have a different scene switch in the room (on the other side of the room) which seems to have no problem turning it off. 
This is the only light in the house that I am having difficulties with, and I have replaced the switch, so two bad switches seems unlikely.  
I have 400 AMP, with two 200AMP panels.  I have a phase couple on one panel. Both the light and the UPB transmitter are on that same panel. 
 was trying to recall any major changes recently in terms of new appliances, etc.  The biggest change I can think of is that we recently swapped out our washer and dryer last month.  The old washer and dryer actually used a single 220V outlet in which the washer plugged into the dryer.  The new washer and dryer both run on 110V (weird, I know), so that 220V outlet is no longer used.
Could it be that the 220V outlet with the dryer was acting as a phase coupler and improving my signal strength or am I chasing down the wrong path?
It looks like Simply Automated makes a phase couple that plugs into a 220V outlet, or I could put one in the electric panel.  I was leaning towards using the 220V outlet once up in the laundry room because I believe I had good signal then.
I have also installed a 3 fans since then, although no idea why that would matter (none of them have been on while testing).
Would you recommend the phase coupler approach?
I would look for noise coming from the load behind that switch.   If the switch responds to on, but not off, the load could be producing noise that cancels out the off signal.
I had exactly this problem on one of my switches that was controlling a LED strip light.   After a lot of experimentation, I found that I could reduce the noise by turning the fixture on to 70% instead of 100%.   
The best way to diagnose the problem is to use Upstart to measure the noise at the switch when it is on and off.    If Upstart cannot contact the switch when it is on, that could be indicating the problem.
I've addressed the noise behind the switch issue by putting in a line noise filter in between the light and the switch. Also have each of the UPS's in the house plugged into a filter to prevent the UPS from "conditioning" the circuit it is plugged into (not by design) and attenuating the UPC signal.
The problem is typically not so much noise, but rather lack of signal.  A filter doesn't do much here, because there is nothing to filter.
So, you need to start by looking at all the loads plugged into the wall near the problem device. What room is the problem device in?  Near a TV, UPS power supply, electrostatic air filter? Really anything can cause a problem.  Think back to when the problem started. Any new appliances near then? 
If you can't figure it out, try this. Unplug everything within 30 feet of the problem switch. Then try it. If it works, slowly plug things in until you find the problem.  It just takes a bit of trial and error. When you find the problem, then add a UPB noise block for the trouble maker.