A friend who really loved the game tried to show it to me, but it kept having server problems. I wonder if that was just an isolated case or if it was frequent, in which case it could drive off users.
It would lose our moves (returning to "Your move" when you'd submitted something hours before).
It would give strange errors "You're using this on more than once device"... erm, no I'm not.
And once it forgot who I was and showed no active games once I logged in again... effectively losing the games I was involved in from my account perspective, but my girl could still see the game and when she nudged it re-appeared on my phone.
And then there is just the non-responsiveness of the server. The start-up splash used to show for less than a second, but now it takes 5-10 seconds if it works at all.
For such a simple app and game it went from being a pleasant distraction to a chore very quickly. As such, our use has plummeted in turn.