Azure Video Communication Service Issues-Incoming calls

We have a video calling feature implemented for our app using Azure Video Communication Service and Azure Notification Hubs. Previously all the outgoing and incoming calls were perfectly working but surprisingly we have observed some inconsistencies on the incoming call during last couple of days. Still, we have not observed any issue on outgoing calls but continuously the incoming call push notifications (Which uses Notification Hubs) are not being received in a consistent manner. Therefore, we are struggling to receive and answer the incoming calls because of that push notification is not received from the hub. Finally, we would like to seek your opinion and idea on what would be the cause for that said behavior. Thanks.