An important point is the distinction between " must " and " can ".

The settings "1,1" under "Master Data | Subjects" in the input field "Afternoon periods/week Min, Max" on the "Timetable" tab forces Untis to schedule exactly one afternoon period. The setting "0,1", by contrast, enables Untis to schedule exactly one afternoon period. If you come across an undesired or even unnecessary afternoon period in your timetable, check the values in this input field. For the same reason, you should try to keep your options open when it comes to double period conditions and enter "0,1" or "1,2".