SERVER-33248 allows a node to choose a sync source with the same lastApplied if it has a higher lastOpCommitted. This leads to sync source cycles, as described in SERVER-39367. This is fixed on 4.2 in SERVER-39367, which reverts the change while introducing a new mechanism to propagate the majority commit point through heartbeats. However, SERVER-39367 is not safe to backport to 4.0, since it increases the likelihood of sync source cycles with nodes that have SERVER-33248. On 4.0, we will just revert SERVER-33248.