It looks like Derpy got ahold of the EQD app's database. Unfortunately the server hosting push notifications and comments randomly got nuked. Unfortunately, our app guy Gameleon who manages the database backups is out of the country until the 23rd of this month.
We managed to recover a older backup, but commenting and push notifications are still a bit unstable until Gameleon works his magic once he returns home. New in app purchases are disabled as well until then to prevent any issues there.
For now, if you want to comment via mobile while the app isn't working, you can still use the usual browser based EQD site. Expect a fix once he gets back home!
Until then, go draw Derpy blowing up servers.