The ? indicator from a connected Thing generally means it is not getting an expected Attribute Value from SmartThings. In this case, the Device Type Handler you are using probably hasn't set a value for "attribute switch".
Login to your SmartThings IDE API webpage, check under "My Devices", open the detail page for the Thing, and check this section, "Current States:
If you don't have a value for Switch that is exactly "on" or "off"... then ActionTiles is going to show "?".
If it's a Water / Moisture sensor, we recommend trying to give it a little manual initialization by wetting across the contacts with your finger or a damp cloth. That will usually force an initial value to be sent to ActionTiles. This may be applicable to other Sensors too, such as Smoke & Carbon Monoxide Detectors.
Otherwise... Please check with the author of the Device Type Handler or SmartApp that is associated with the Virtual Switch. Perhaps a value hasn't been initialized?
The ? indicator will also appear if your Location has become paused or disconnected from SmartThings. This cause is more obvious, however, since you'll see many Tiles with "?", not just isolated cases.
Customer support service by UserEcho