first up NoMoreURLsAvailable is very common now it is not unusual to see between 8 and 16 hours a day work only.

With the above there is a tendency to run nodes down towards zero so you may be seeing the poorer quality, smaller buckets and re work buckets coming through and effecting your dns averages.

I would say that anything in the 2-10% range is normal. This is the range I see running 60 small nodes. most of the time it is in the 4-5% range but even though these all run on the same rig I see some that go well outside these limits on occasion. I have even had a warning email a couple of times. I re-start nodes every 24 hours to get a better feel for error rates