Oh and for what it's worth, I've also looked through the logs for this node, and the oldest error in the logs seems to be:
[0000] 06 Nov 22:10:53.260 * pri=ERROR t=Thrift:16 at=CustomTThreadPoolServer.run Error occurred during processing of message. java.lang.RuntimeException: java.util.concurrent.ExecutionException: java.lang.RuntimeException: org.apache.cassandra.exceptions.ConfigurationException: Column family ID mismatch (found 3ed23e80-84d3-11e5-83b3-0fc0205655f5; expected 3ecce750-84d3-11e5-bdd9-dd7717dcdbd5) Then the logs show a compaction, and then the UnknownColumnFamilyException starts occuring.
