There are two ways that the app does not show holidays anymore.
Selecting the right calendar.
The app offers the possibility to display all appointments of an explicit calendar. You do this as follows -> open the app -> open the menu -> scroll down to "general" -> choose "Calendar" -> choose the calendar you really want to see. Leave out the holiday calendar.
Deactivate holidays in ios
You can also deactivate the holidays in the ios calendar. do this as follows: open your ios calendar -> press "Calendar" at the bottom of the screen -> deactivate the holiday calendar.