The application runs a data index on words that appear in the app.
If you type a search term quickly and execute the search before the app has a chance to reference the data index, it will run a legacy search that simply renders all results for that term. For Express and Enterprise events, the autocomplete search option (reference the data index) is not available until the app has received at least one update (not available on first download of event).
If a you type a search term more slowly, including a partial word search, the app will reference the data index in an attempt to provide you with autocomplete suggestions. Partial word searches that reference the data index will render results for the most likely autocomplete result; thus, not necessarily rendering every result for that term that exists in the app.