Hello,
Thanks for your report. I could reproduce the problem with your steps. After importing the .ics with Google Calendar, the UID is not in the calendar storage:
> adb shell content query --uri content://com.android.calendar/events | grep -i "Test 6"
Row: 60 originalAllDay=NULL, account_type=bitfire.at.davdroid, exrule=NULL, mutators=com.google.android.calendar, originalInstanceTime=NULL, allDay=1, allowedReminders=0,1,2, rrule=NULL, canOrganizerRespond=1, lastDate=1578787200000, visible=1, calendar_id=9, hasExtendedProperties=1, calendar_access_level=700, selfAttendeeStatus=0, allowedAvailability=0,1, eventColor_index=NULL, isOrganizer=0, _sync_id=NULL, calendar_color_index=NULL, _id=581, guestsCanInviteOthers=0, allowedAttendeeTypes=0,2,1,3, dtstart=1578700800000, guestsCanSeeGuests=1, sync_data9=0, sync_data8=NULL, exdate=NULL, sync_data7=NULL, sync_data6=NULL, sync_data1=NULL, description=-::~:~::~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~:~, eventTimezone=UTC, availability=0, title=Test 6, ownerAccount=pina@example.com, sync_data5=NULL, sync_data4=NULL, sync_data3=NULL, sync_data2=NULL, duration=NULL, lastSynced=0, guestsCanModify=0, cal_sync3=NULL, rdate=NULL, cal_sync2=NULL, maxReminders=5, isPrimary=1, cal_sync1={"type":"SYNC_TOKEN","value":"1578401281"}, cal_sync10=NULL, account_name=pina@example.com, cal_sync7=NULL, cal_sync6=NULL, cal_sync5=NULL, cal_sync4=NULL, calendar_color=-5592406, cal_sync9=NULL, cal_sync8=NULL, dirty=1, calendar_timezone=NULL, accessLevel=0, eventLocation=NULL, hasAlarm=0, uid2445=NULL, deleted=0, eventColor=NULL, organizer=first.last@googlemail.com, eventStatus=NULL, customAppUri=NULL, canModifyTimeZone=1, eventEndTimezone=NULL, customAppPackage=NULL, original_sync_id=NULL, hasAttendeeData=1, displayColor=-5592406, dtend=1578787200000, original_id=NULL, sync_data10=NULL, calendar_displayName=Persönlicher Kalender
Note that uid2445=NULL
. DAVx⁵ never gets the UID from the .ics, so it has to create an own UID and continue.
(I have also tried aCalendar+, same result here.)
So this is a problem of the calendar app. I’d recommend to get a calendar app with support and then asking about whether they can implement that.
Does that help?