This is because of a system property - glide.service_portal.search_as_you_type_behavior
This property has 2 values - Suggestions & Typeahead.
If the value is set to suggestions, then typeahead will not work.
In addition to this, you also need to check with the property - glide.search.suggestions.enabled
When you switch to typeahead, make sure to set the above property as false.