[Firebase_database] Receiving _InternalLinkedHashMap where should be a List

[jesusc0310]

I'm creating an app which backend is on Firebase Realtime Database, i'm querying for data from a list from 20 to 20.
First 2 times i get a List as expected, but 3rd time I get an _InternalLinkedHashMap instead.

Here i call my list, that was imported from a well-formed json and it's a 1000 object list

final dbData = await _db
        .child(child)
        .orderByChild(childKey)
        .startAt(_lastIndex)
        .limitToFirst(_limit)
        .once()
        .then((snapshot) => snapshot.value);

After that, i added this code to prevent an unhandled Exception, cause _InternalLinkedHashMap<Object?, Object?> is not a subtype of List<Object?>

if (dbData is List) {
      data.addAll(dbData.map((e) => SampleModel.fromJson(e)).toList());
    } else {
      dbData.forEach((k, v) => data.add(SampleModel.fromJson(v)));
    }

I don't know if this is usual or not, my query works properly, but received values are not as expected.

What can i do to work this response just as a List and not as a _InternalLinkedHashMap?