A bug has been reported in Universalis on iOS 6. It affects iPhones and iPods only, not iPads. The effect of the bug is that in the calendar display every day is blank. The days are there, and they work, but they have no text.
This bug has been corrected. An update for the Universalis app will be available from the App Store on Monday 22 October, and the App Store application on your device should offer it to you automatically then. (The corresponding update for Catholic Calendar has been available since 11 October).
Meanwhile this post describes a way round the bug.