Activate Google Cal Sync

Google Cal Syn

is for subscribed cals sometimes deactivated, so go to

https://calendar.google.com/calendar/u/0/syncselect

Attention

It can take up to 48h that google will fetch changes from a calendari. You can force a manual sync with

https://github.com/derekantrican/GAS-ICS-Sync

Or use a program like ICSx5 under Android

https://icsx5.bitfire.at/