I run a Wiki on a Mini Mac server. Set-up had wiki's, Calendars all working. Then one morning it went off line and when logging in was painfully slow. As this was a business Wiki I quickly did a carbon copy to the second internal drive and it all worked again. apart from the calendars. I get the 'Getting Events from Server' message and :
caldav-8009 Failure: twisted.internet.error.ConnectionRefusedError: Connection was refused by other side: 61: Connection refused.
From ICal logs.
The server is also constantly indexing that is a worry.