as said, “unavailable” only tells you so much, it’s not a general judgement for all times (outside the issue you describe).
The value in that screenshot is: the device+sim can register with the IMS stack at the provider, that is good, it’s the basis for any of the Vo* things.
If you’re getting adept at reading adb logcats there could be a clue what’s hindering the tunnel building for vowifi. I did FP3 (not FP6) debugging with ims things and this user had for whatever reasons missing libs.
If vowifi is a widespread issue on the device I’d think it should’ve made its way to the backlog tracker on the FP6 tag.