Dist cache can lost data if the primary and all backups are lost at the same time. To detect such data loss, they are monitoring the tatal sum of entries from all nodes using JMX. If the sum reduces by a considerable ammount, data loss (by lost a segment) is concluded. But they found a case that the sum increases, not decreases, after failed state transfer. This is probably caused by an extra backup segment that hasn't been cleaned up when the last state transfer failed.