Week Calendar supports Full screen mode, like the iOS' Photos app.
When full screen mode is enabled, the top and bottom bar (configurable) will show on top of the contents of the calendar, until they are dismissed by either a single finger tap or a double finger tap, depending on your settings.
The first week of the month view is hidden!
This happens when you have Full screen mode enabled: the top bar will fall over the contents until it is dismissed.
If you do not want this behavior, please set Settings > General > Full screen to OFF.