Had the same issue when trying to add a second user. Deleted the secondary user via the app and the problem was resolved. Stay away from adding users...
I just had the same issue. Car is 5 months old and has had multiple accounts on it since new, with no issues until now.
I disconnected the 12V battery for 3 minutes then reconnected and it all seems to be working fine again now. Seems that its the Porsche equivalent of CTL+ALT+DELETE ...