SERVER-65300 accidentally removed this piece of code. Though the reason they added initially is due to SERVER-54191 but that fassert mentioned in SERVER-54191 has been changed to uassert. But looking closer into the oplog buffer code, it seems it's illegal to start the replicated oplog buffer collection when the node is no longer primary, otherwise we would end up hitting other fassert and non-retryable error code like mentioned in BFs.