I use Google Calendar to display the availability status of an airplane that I share with four others. About a month ago, the web page with the embedded calendar stopped displaying events. I also noticed that events don’t show up on other calendars e.g. the local high school’s vacation schedule.
It took a while to figure out what they broke, but it looks like you can’t view events on embedded calendars unless you are logged in with a Google account. Since I don’t use Google on Safari, they won’t let me view my events. When I open the page on Chrome, where I am logged in, I can view calendars. So now you know.