Alice recently updated her iPhone to iOS 13 and she can't use her calendar with it. When it launched, it was kind of a mess and Leo says that Apple is updating iOS 13 almost weekly since it came out. Vs. 13.2 is about to come out, which not only will solve those problems but will have an update to the camera as well. Leo recommends Fantastical. It's much better. BusyCal is another.