I'll try and get a sample together but it's my son's birthday tomorrow and last day of work plus out tonight so probably be next week before I can..
Put simply, all roads lead to MessageTime which is the date time property. Both Hour and ReversedTime are read-only properties that refer to MessageTime. As you can see, whilst I'm displaying ReversedTime with a title of Date, I told it that the grouping was to be on Hour which matches with the collectionviewsource's own grouping. However, I don't think there is a check done or because I've initiated them explicitly in both cases and not using a shared resource, it ends up trying to add a second Hour grouping which causes the crash.
Put simply, all roads lead to MessageTime which is the date time property. Both Hour and ReversedTime are read-only properties that refer to MessageTime. As you can see, whilst I'm displaying ReversedTime with a title of Date, I told it that the grouping was to be on Hour which matches with the collectionviewsource's own grouping. However, I don't think there is a check done or because I've initiated them explicitly in both cases and not using a shared resource, it ends up trying to add a second Hour grouping which causes the crash.