After upgrading to SmartThings app 2.2.0 (on an iPhone with iOS 10.0.1), I noticed that sometimes the widget wouldn’t actually do the action. Instead of showing the flash of green and turning my lights off, it would flash red instead. If I go into the app itself, I can use the widget again. I’m guessing that the widget now only works as long as the app is actually running, and once it is quit the widget no longer functions. That’s a wild guess, though.
This definitely started with 2.2.0, not with iOS 10. At least I"m pretty sure, anyway; they both cam out at about the same time, but I only noticed this problem last night, and have been running iOS 10 since Wednesday.