Pages 1 to 13 are missing from ED 3b, in RG9/3779, Sunderland Sub-district. You'd need to look at the actual census to check whether this is part of Sunderland or Bishopwearmouth parish. There are 855 pieces in 1861 that are known to have missing pages, but the list on FindMyPast only shows about 100 of them. It appears to be an old list that has never been updated.