Umbraco 8 Examine/Lucene query returns no results in code but searching from the backoffice works as expected

Question

I'm trying to do a simple Lucene query in a fresh Umbraco 8 site (8.13.0, Examine 1.1, Lucene.Net 3.0.3).

I'm trying to get all documents of a specific type but I get no results back.

ExamineManager.Instance.TryGetIndex(Constants.UmbracoIndexes.ExternalIndexName, out var index);
var searcher = index.GetSearcher();
var query = searcher.CreateQuery()
                    .NodeTypeAlias(BlogPost.ModelTypeAlias);
var result = query.Execute();

var rawQuery = query.ToString(); // == "{ Category: , LuceneQuery: +__NodeTypeAlias:blogpost }"

// result.Results.Count == 0
// result.TotalItemCount == 3
// result.TopDocs.TotalHits == 3

If I take the raw Lucene query +__NodeTypeAlias:blogpost and stick it in the search field in Examine Management in Umbraco I get 3 results as expected:

Why isn't it working from code? (What am I doing wrong?)