Previously desktop-qt5 desktop helper was using downloaded package and was not download packages again if they are in apt package cache. Now that feature is broken.
snapcraft a desktop-qt5 app.
Clean using snapcraft clean
now snap it again
it will download all the artifacts again in order to build .snap file.
This is stupid and annoying.
this was the bug i have reported Bug was fixed before (not on my report but somewhere else ). Now snapcraft clean is behaving same again.