I had one really strange bug on the ipad once. My opponent moved a knight, and the knight just vanished into thin air. Then, I was unable to move anything myself.
I closed the app and restarted it, but the game was gone.
Edit: Just found the game: http://www.chess.com/livechess/game.html?id=203843062
As you can see, that last knight move never actually happened.
I play on Chess.com mainly on the iPad and iPhone and thought I could give a brief run down of the problems with the apps for blitz-style play, and how these impact on the rest of the Chess.com community. The rise of these apps (and other mobile platforms) may explain why a lot more games are being "abandoned" than in the past.
1. Secretly lost connectivity bug
There is a bug in the iPad and iPhone app that causes my side to disconnect from the main server. On my screen it looks as though my opponents clock is running down, but on the server my opponent has moved and it is my clock that is running down. Eventually I lose, either on time or via a message saying I abandoned the game.
In this scenario, the app does not display the "Reconnecting..." alert. The only way to discover the problem is to attempt chat - your message will not be shown after you hit the "Send" button. Other internet services such as browsing work fine.
This is obviously also annoying for my opponent and I think about 1 in 10 of my games end this way. But I never get this problem using the desktop browser.
2. Connectivity generally over 3G
I have given up playing over 3G (in London, UK). Too many games were being lost due to the connection going down and the app failing to reconnect the game when the connection came back up. Maybe one time in 10 the app would reconnect successfully and allow me to complete my game (minus 1-2 minutes on my clock).
Again, annoying for opponents.
3. Moving on the iPhone
There are four ways to move on the iPhone. None is entirely satisfactory.
The four are: Slide the pieces; or point to the piece and then the destination square. And in both cases a submit button can be used to confirm the move.
Pointing is more reliable than sliding, I find. But mistakes can still happen because the screen space is small and once your finger is on the screen you can't see what's underneath it. This is especially true for 1-space moves. The Submit button seems to be the answer, but guarantees a loss in tight blitz play - it adds about a second to each move and, especially when you are trying to move fast, does not always respond to the first hit.
Again, mistaken moves can ruin a game for both players. But maybe the time problem won't be minded so much by my opponents!
Anyway, for all the problems, these are great apps. Well done Chess.com!