Mapbox geocoding: half empty address results

When geocoding via QML GeocodeModel using mapbox plugin some search strings yield empty address results (only country and state are set) when they should at least yield city or street name. Look at the  screenshot "A": the first highlighted result is actually what I am looking for but text description is not helpful at all. If we are to reverse geocode coordinate of this location data it will yield a concrete address (screenshot "B") and this address is what I expected to see in direct geocoding (minus unit number). Plus, I tested osm geocoding plugin a little and did not encounter such problem with it. 

Not sure if it is a Mapbox bug, Qt plugin implementation bug or my poor understanding of the problem but have to start somewhere.  

Steps to reproduce:
Using attached program input "niskayuna, usa" or "frank".

Expected behavior:
All result addresses have either "city" or "street" properties set

Actual behavior: 
"niskayuna, usa": the first result has only country and state set
"frank": the first six results have only country and state set

In general, such cases are not uncommon, especially when using composite or ambiguous search strings (screenshot "C"). As you can see, such results are not presentable to end users. 

Upd. I am inclined to think that it is a plugin bug because Mapbox's geocoding-feedback service provides the same results but with properly filled info: city or street are filled. See screenshots D vs C.