I've recently upgraded to Oreo and just noticed that there are no more custom label sound/vibration settings for Gmail?!
Seems gmail is using the new concept that Oreo has, central app notification management which has only one setting per application.
The behavior on the newest gmail app release (184.108.40.206150130 at the time of writing) is apparent only on Oreo.
As i'm using the phone for business i'm reluctant to try and play with downgrades to check where they started to use oreo "features", anyone that could check?
Anyhow, i was extremely dependent on the different notification sound per label/priority inbox so this killed my productivity...