Currently the lease mechanism in DocumentNodeStore/mongoMk is based on the assumption that the clocks are in perfect sync between all nodes of the cluster. The lease is valid for 60sec with a timeout of 30sec. If clocks are off by too much, and background operations happen to take couple seconds, you run the risk of timing out a lease. So introducing a check which WARNs if the clocks in a cluster are off by too much (1st threshold, eg 5sec?) would help increase awareness. Further drastic measure could be to prevent a startup of Oak at all if the difference is for example higher than a 2nd threshold (optional I guess, but could be 20sec?).