I'm using Kal calendar, which is open source. The issue here is dates are not rendering properly with iOS 10. Please let me know if you have solution or what is causing the issue.
Seems to be an issue with the system font name. I replaced
UIFont *font = [UIFont boldSystemFontOfSize:fontSize];
UIFont *font = [UIFont fontWithName:@"Helvetica" size:fontSize];
in KalTileView to get it working.