Long lag before showing events from remote Google calendar (even if offline)
I noticed that Calendar tends to take about 30 seconds to show some of my remote web calendars (simple iCal-style subscriptions), and interestingly this happens even sometimes when I am offline (they still show after a certain time). The calendar contains about 150 events per time but there is no reason it should take this long to load.
Also, this behaviour is slightly dangerous, as without any way to know Calendar is still syncing it makes it easy to miss events in some days (especially when checking calendars quickly, as most other calendars load much earlier).
To be clear, all these events are properly cached and shown in the GNOME Shell calendar integration.