It would seem (if the metrics registry is accurate) that replica fetcher threads can persist after a leadership election. Even when the broker itself is elected leader. This also seems to occur after a reassignment too (as evident by the 5 different thread entries for the same partition in the registry)
This leads to inaccurate MaxLag and ConsumerLag metrics to be reported. Since it's whatever the last reported value is. Restarting the offending broker clears these at least.
