Actually, it could be a channel issue.
The new “friends of Hue” Battery free switches are kind of an odd design as they Are using Zigbee green power, not the full zigbee 3.0 clusters. In order to save energy, these are teeny tiny pulse commands. And so far most of these devices have come out working only on a choice of two or three of the ZLL channels. (See the Illumra Details above in post #14.)
Since smartthings also used the ZHA channels, It’s quite common for a smartthings hub to be on a zigbee channel like 14 while the switch is on 25.
So adding one of these green power devices is not like adding a lightbulb which will find the right channel when it joins the network.
While zigbee 3.0 itself is backwards compatible, there are some exceptions for devices which would have been green power profile devices prior to Zigbee 3.0. (And of course there’s also a touch link issue, although that doesn’t apply to these particular devices) In particular, the manufacturers of green power devices are allowed to limit channel changes to manual touch patterns rather than making the device smart enough to do it on its own, which would require power the device doesn’t have.
All of which is to say that first before you do anything else you have to make sure that the channels match for these green power devices.