Azure Notification Hub - push to one user on multiple devices

I have built a server side version of Notification Hubs according to Azure tutorials. (the following applies to APNS only)

Users register for push notifications using their device token. What I do during the registration is that I tag the registration with our internal database ID. So if the user is using two devices under one account we end up with following registrations:

1. Registration 1. - device token XYZ - tagged with id 123
2. Registration 2. - device token ABC - tagged with id 123

However whenever I send the push notifications only one of those devices receives the push notification. I was thinking that all of those devices would receive the notification. Is there any known limitiation why this would fail for two devices being used by one user?

See both registrations listed in here - copied from device registrations screen:

Apple (APNS)    Template    identityId:5e8dc2e9-e4dc-4c65-bf68-f5847534c9fe 202F74E526A3C7D96E406BA78E356735E6E7EEC841731325366453CC048335D7    1540672349737584107-5893757784548740535-1   31.12.9999 23:59:59
Apple (APNS)    Template    identityId:5e8dc2e9-e4dc-4c65-bf68-f5847534c9fe 5E635F6A261FDA223AC2EA67DB1DC0AC24E04129DB0B8B77C4958E4C69D6EC2D    2450579646911095780-3631197759391298147-2   31.12.9999 23:59:59

The problem was that our device was in DND mode - so the notifications were not visible. After setting the device to normal - everything started working as expected.