With the patch applied, healthcheck.leader.interval set to 60 seconds and cluster.leader-session-ttl set to 100 seconds, I could no longer produce a situation where multiple nodes were active at the same time.
With this configuration, each lnd node creates an etcd lease with a time-to-live of 100 seconds. This lease is kept alive at intervals of one third of the initial time-to-live. So in this case it is kept alive every 33 seconds. When a node loses its connection to the rest of the cluster, it takes 27-60 seconds to initiate a shutdown. And it takes 66-100 seconds for another node to take over. So in this configuration there is no room for overlap, so no chance of two nodes being active at the same time.
healthcheck.leader.interval
set to 60 seconds andcluster.leader-session-ttl
set to 100 seconds, I could no longer produce a situation where multiple nodes were active at the same time.