When modifying a Recurrence Personal appointment the appointments are being duplicated after the autosave.
steps to dup:
Create a personal appointment with daily recurrence (starts 04/04/2018 - 04/08/2018) and save
Re-open first appointment in the series then open the recurrence settings, add 2 days (for example 04/04/2018 to 04/10/2018) and then WAIT for the autosave. The appointments will be dubbled.
Even if you do not open the recurrence settings, but just edit the appointment and wait for autosave it will be duplicated.
There are also many variations once autosave occurs (for example, you then cannot delete all the instances, it will leave the last instance) Basically autosave seems to not work for recurrence personal appointments.
This has been reported to engineering