So moving forward with this.. (apologies for the side distraction) the devices you are using are older Z-Wave?
Note: devices like FGS-222 are not on the compatibility list so your mileage may vary with those. I have not had good experiences with dual switches - My Aeotecs were far too slow, I also tried Qubino ZMNHBD3 as well. Fried that last one myself . Eventually ended up embracing the dark side and went with proper smart switches (our area Toggle Style is pretty common).
One thing to be concerned about is older Z-Wave (NOT ZW+) can bog things down in general thanks to hub polling requirements and the "routing" rules of the devices themselves.
Most of the Z-wave devices are 4 year and older Fibaro relays. But they seem to be working reasonably reliably. It seems (and this is just a gut feel), that the issues relate to the Aeotec devices (in particular the Heavy Duty switches). Strangely, the distance from the hub doesn't make a difference. E.g., the one Aeotec Heavy Duty switch is less than 3 meters from the hub and its reliability is one of the worst.
Since the Z-wave network has not been improving and devices would not respond half the time, I've decided to exclude all devices joined with S0 security. (With a few I won't have a choice, such as locks.)
I'm almost done excluding S0 devices Ater that, I'll leave things overnight before I start including devices again.
(I don't suppose it counts for much, but I did not have these issues with my previous hub. The network has been running fine for at least the last 3 to 4 years.)
. Eventually ended up embracing the dark side and went with proper smart switches (our area Toggle Style is pretty common).
