Other users that have encountered this found that reinstalling worked just fine and then the app loaded without issue. I don't know if it will have any impact if I release an update to MobileSheets, as this problem occurred with no changes to MobileSheets (updating the OS seems to be the source of the problem). I'm not sure why the installation is stalled for you though - I'm assuming you have already tried rebooting the device and then trying to install the app again.
Mike
Mike