Caldav autosync iOS11 dosnt work

i have any problems to sync my nextcloud calendar automaticly. the sync manually is works fine but syncing every 15min dosnt. I habe multible calandar on my iphone and the 15min timesync works fine, only the nextclout dosnt sync (is the only caldav). Is there any problem in iOS?



Did you ever find a solution to this problem?

Thank you!