I've also been experiencing this issue and would love a solution. Voicemail notifications have never worked for me on my Pixel 3. It took me quite a while to notice, because I don't get that many, which makes it all the more onerous, because I don't want to have to check all the time. I do have the My Sprint app (which I assume is what you are referring to as the Sprint Hub app).
The verifying account information screen shows when I first install and doesn't go away until I touch the screen at which point it advances to show me the personalization screen and an initial voicemail message, but doesn't show me any of the actual messages in my voicemail box.
Nothing to report at this time. Last I heard the Big G was cooking up a software release.
Any updates on a fix yet? Thank you!