This issue is not the same with 'Azure Notification Hub registrations disappear when sending a notification'.
First of all, I can make sure it is not a certification issue. Because normally it can receive the notification without any problem.
The process to reproduce the issue:
Install the app and register the push notification. (We can see 1 record from the 'Service Bus Explorer')
Uninstall the app
Reinstall the app and register the push notification
Repeat step 2 and 3 several times (we can see some registrations from the 'Service Bus Explorer')
Send a notification
Sometimes, all the registrations disappear. Sometimes, the last one will be left.
Does anyone have any idea about this issue?