I can't see one of my Live calendars in Outlook anymore.

[Windows Central Question]

Recently, a shared live calendar doesn't sync in Outlook anymore. I've been using it for years, and from one day to another it disappeared from my list of calendars in Outlook. I can still see the calendar and its events online, but not in Outlook. When I create a new calendar online, it is also synced to Outlook.
Anyone who has the same issue? And knows the resolution to this?
Thanks!