None of us should underestimate how much other 2.4 Ghz interference (in my case, primarily WiFi) may cause the Zigbee signal to appear intermittent based on what Zigbee channel your Smartthings hub initially set itself to.
I have 2 of the KoF Wink fan controllers. One worked fine from day one. The other was intermittent off and on from day one. Finally, it went to being intermittent permanently.
I tried the following fixes in several different permutations over a week to no avail
1)Restarting hub twice
2)Resetting fan controllers with off/on breaker toggling until customary blinks were received, but not on intermittent fan
3)Deleting both of the controllers from Smartthings and re-adding
4)Hard reset of hub
Finally, decided to research Zigbee WiFi interference at the below link.
Discovered my WiFi AP was set to auto channel and had set itself to channel 1. Smartthings Zigbee channel was set to 14. Because of the way the Zigbee channel numbers are offset, WiFi 1 and Zigbee 14 were too close. As soon as I set the AP channel to 11, the intermittent fan controller responded and has been working consistently since then.