I was a lifelong renter until 3 years ago when I bought my first home. I went all out and my "starter home" is a Queen Anne victorian. As with most homes built before AC wiring was a thing, automation comes with its unique challenges. (Your zwave switch requires a neutral? ha!) All in all I've been pretty successful but there is this one sconce on the main stairs that has always given me trouble. It does not appear to have a wall switch anywhere, and every smart bulb I put into it either fails from the get-go or fails shortly after installation. Some of them just sit there and flicker on and off right away, others start doing it a bit later. Since it's the main stairs, some illumination is a good idea, but having a regular light in there keeps me up at night since it shines into the master bedroom if the door is open. I even went so far as to purchase a Hue hub and migrate all of my zigbee bulbs off of HE onto Hue to try to resolve the issue, nothing. (Though the Hue hub was still a good idea.) I finally just took the bulb out and decided to risk a tumble down the front stairs.
Today I thought maybe in my collection of non-smart LED bulbs I had a dim one that would give me enough light to see but not disturb my sleep. The sconce is at eye height and faces up, so I have to put the bulb in without being able to see the base. Sure enough the dim bulb started to flicker. As I went to unscrew it, the flickering stopped. Moved my hand, it started again. Then stopped. It finally dawned on me that perhaps there was an old photo sensor in the fixture and that my hand casting a shadow was causing the change. I dragged out a ladder and positioned myself so I could see into the fixture itself. Sure enough, there was a screw-in photo switch! And an old one to boot. It never worked enough to actually control the light but all these years it was causing some lights to flicker and obviously causing the smart bulbs to eventually disconnect from the network. Yanked it out, put a Hue bulb in, good to go!
I guess the moral of the story is... don't be a lazy ■■■, get out the ladder and look inside 
