macOS 10.14.6, Calendar.app 11.0 (2245.5.2)
Less than an hour ago, I brought Calendar.app to the foreground (I usually keep it running, hidden in the background), and most (8 out of 12) of my Google calendar contents were completely gone. All calendar names are still listed/checked in the Calendar List pane on the left side of the window. I can't figure out why some are still there and some aren't. I rebooted, but still the same problem. If I view my calendars on the web at calendar.google.com, all contents are present & normal there. I use Mail.app to read my gmail account, and all email is present & acting normally. The Google Calendar IDs continue to match in Calendar.app and in the prefs at calendar.google.com. No errors are being shown to me in the UI, and I don't see any errors in Console.app. I have never had this happen before.
Very mysterious! Any suggestions?