I was having the hardest time getting my hub to talk to a dimmer switch in my bedroom which is only 25 feet away, and I think I figured out the problem.
First, some communication was happening, because the switches (I tried three of them) were recognized after a few attempts to add them to the network. But after that, they became unreachable.
So I bought an Aeon Range Extender ($20) and placed it almost precisely halfway between the hub and the switch, in the only available location (the house was built in 1969, but it still doesn’t have that many outlets).
The hub could see the repeater fine, but still could not talk to the switch. I started experimenting with various repeater locations with an extension cord, and found that other locations worked—but none that was feasible for a permanent installation. I tried other plugs at various locations but they were all too far or poorly placed.
Finally I tried one plug next to the bed which I had not considered because it is further away from the hub than the switch is. This one worked!
So then I realized that all shorter but non-working paths were going through a large mirror which covers an entire wall about 5 feet in front of the switch (about 5 feet wide and 8 feet tall). Is it well known that mirrors block the 900MHz signal? I had no idea.