One of the metrics reported by the ConnectionPool is totalRefreshing, which refers to the number of connections that are scheduled for a refresh. Connections may get scheduled for a refresh due to hitting a timeout (see here), or after getting returned to the pool (see here).
It appears that the connection pool may not accurately report the number of connections scheduled for a refresh. For example, the following shows the increase in the number of hello commands (due to refreshing connections), but does not accurately report totalRefreshing.
This ticket should investigate this possibility and provide fixes if necessary.
This ticket should introduce a new, cumulative metric that tracks the total number of refreshed connections (e.g., totalRefreshed).