I have the same problem. Also have DAVdroid + OpenTasks installed with LineageOS.
Is there any way to do a backup of the calendar settings? I tried using Titanium Backup, but was not able to restore the settings after all calenders disappeared.
[taken from issue tracker]
Concerning the onCreateView in the AddCalendarDetailsFragment.java:
Some Outlook calendar-exports feature a X-WR-CALNAME property (as e.g. Link ) and if parsed, this could be a reasonable suggestion for the title of the calendar.