One other issue (quick feedback): When creating a new ics calendar, when enters the URL and the absolute path of the URL becomes the cal’s name, for posteo this is something like /calendars/ics/dasd882342332234234 as cal name. Would be better if one could enter Name and URL when adding a new ics.
This is a duplicate of https://forums.bitfire.at/post/12711. Please follow up there. Unfortunately, I don’t know why Android starts synchronization when Internet is not available yet.