can't get voip push token for some devices

My app use VoIP push andregister for VoIP notifications using PKPushRegistry on launch.

Then push credentials updated for PKPushTypeVoIP type in most device.

But some devices, push credentials never updated and even invalidate delegate isn't invoked.

In this case, I can't receive any notification for VoIP token request.

for Just some devices(os version : 10.2 or later), for VoIP push token.

Request for APNS push token is always succeeded.

I wrote the code just the same as code in https://developer.apple.com/library/content/documentation/Performance/Conceptual/EnergyGuide-iOS/OptimizeVoIP.html

And It works when restarting device, So It looks like OS bug...

Anyone else having the same problem?