i ran some LOSA projects a couple of years back. In one survey of 180-ish flights the error rate was 6/sector. In another survey looking at flight through the WOCL the rate was 10/sector. If you look at the range, we were seeing anything from 2-22/sector. No sector was error free.
That matches pretty close from the LOSA I was involved with a year or two ago, about 6 to 10 per sector, with some flights reaching into the mid-twenties.