partitionLeadershipInfo is the in memory cache of the controller that keeps track of every partition's "last elected" leader and isr. On controller startup/failover, this cache is bootstrapped only with those partitions whose leader is alive. This causes the leader and isr cache to be initialized incorrectly causing other state transitions related to new broker startup, existing broker failure to not work correctly. For instance, it does not allow the controller to send the list of all replicas that exist on a broker to it during startup.
Another bug during controller startup is that it invokes OnlinePartition state change before OnlineReplica state change. This also breaks the guarantee that the controller sends a full list of replicas to a broker on startup