On current project - Customer requires that all active activities owner be updated when the parent (regarding) is changed.

Noticed on Appointment when updating the relationship behaviour from Parental to Configurable Cascading - Assign - Cascade Active -

All other activity types respond as expected but only Appointments Owner was not updated.

When investigating with MS Support they said the below:

they confirm this is by design limitation, Because if you create a record from Appointment main form, then assign to a Lead, there will be no issue. So, for your specific situation, they come up with a work around that adding a custom script

when the user sets 'Assign' to cascade active, only the active records are re-assigned. Based on the behavior, Open and Completed appointments are not considered 'Active'. Only the scheduled ones are. So Assign behavior is correct. Now let me explain why are certain appointments created with Scheduled Status and some with Open Status.

We have Appointment Scheduling feature. When a user creates or updates an appointment, this feature checks whether all parties in the appointment are free during that timeframe. If yes, then it creates an appointment with 'Scheduled' Status, otherwise it shows a notification telling the same. This feature is only available in main form and not the on the quick create form. The default save (on quick create) creates appointment with 'Open' status. Hence, it isn’t re-assigned as it isn’t an 'Active' state.

Solution I was given was JS to be run on the forms as a workaround.