The lowest VLAN ID is always monitored by ClusterXL (i.e., CCP packets are expected to be sent/received on this VLAN interface). If there are no CCP packets on a monitored cluster interface, then by design, a cluster will fail over.
The lowest VLAN interface is not always used. Meaning, although this lowest VLAN ID is configured, no traffic is passing on it, which in turn means that no CCP packets are passing on that monitored VLAN interface. This will cause unexpected failovers and cluster instability.