No documents on an index

I have a collection (‘User’):

  name: "User",
  history_days: 30,
  ttl_days: null

which is populated with some documents.
I have an index (allUsers):

  name: "allUsers",
  unique: false,
  serialized: true,
  source: "User"

Selecting the allUsers index gives:


I have other collections and indexes defined in the same way which do retrieve the documents.
What could be preventing this index from displaying the documents? thanks …
UPDATE: Self-solved. Deleted old and re-implemented allUserNames index. Name now matches schema.