i asked jolla about the problem. latest statusupdate:

I am trying to get the status from our R&D but many of the folks are on holiday. This fix seems to require more fundamental changes than expected. R&D wrote in the bug report: "Currently, the calendars for a Google account are synced through the Google APIs. We should look to syncing Google calendars through a CalDAV plugin instead, as the Google APIs are limited in respect to calendar syncing".

Unfortunately there is no ETA yet. I am doing my best to get that at least.

let's see if they can fix it with the next update in september