Thanks Victor. FWIW, we are (already) using version 4.6.4.
iCal link: https://calendar.google.com/calendar/ical/01lr07idsognuqto55ubf89aqk%40group.calendar.google.com/public/basic.ics
It appeared to have imported successfully once (initially), and then not again.
See attached screenshot of Event Aggregator System Status. FYI, the “current usage” shows 100 out of 100. This is due to this calendar attempting to reimport repeatedly throughout the day, without success.