If ShowWeekGroupHeaders="True" and we have AllDayArea, the extra line from week group header is not taken into account by the AllDayArea and that shifts the last appointment in it to show in the day area.

The XAML team has recently reviewed this issue and will not be addressing it as at this time the team is focusing on the bugs impacting the highest number of developers. If you have encountered this issue and it is blocking for your work please contact us through the support ticketing system with details on your setup and a reference to this item.