What I see when I look at your vbucketmap in the logs is a cluster that has not rebalanced entirely. It looks like perhaps a rebalance was started and perhaps stopped for some reason?
You should be able to initiate anther rebalance and once it's completed, your data should evenly distributed again, taking the load off the single server. Other than that, the client looks healthy, although I do see some key not found in your logs - this could be expected, however.
If you continue to cluster issues, Cihan can probably help out more than me given his experience there.