We have encounter a strange problem that notifcation service extension may lead to duplicate notifcations.
Our app used Notification Service Extension to improve user experance. As shown in the pic, it is the same notification receied at the same time. The only difference is one has Image while the other not. We have checked out backend server, the log shows that the notification had been sent only once. Many users only received the notifcation with image.
We have checked many ways to reproduce this situation but failed. Our user, however, give us a feedback about this issue happened again.
According to our user, one happened on iOS 13.1.3, the other happened on iOS 13.3