Why are push notifications not being received on iOS / Android devices when sent by segment?

If push notifications are not reaching iOS/Android devices when sent by segment, but are received when sent by HWID, the device most likely does not match the segment criteria, or it is not in a subscribed state.

To resolve this:

1. Check the segment criteria. Confirm the device actually satisfies every condition of the segment. For example, if the segment filters on a tag such as Phone number, that tag must have a value on the device. Open the segment in Audience → Segments and review its definition.
2. Check the device/user state. Go to Audience → User Explorer and search by User ID, HWID, email, phone or push token. Open the user, then the Devices and platforms tab: it lists every channel linked to that user with its Subscription status, Last active date and the tags that actually have values for that channel. Use the Segments tab on the same profile to see whether the user is really a member of the segment you are sending to.
3. Check marketing vs transactional and frequency limits. A marketing message respects unsubscribes, frequency capping, the silence period and the global control group; a device excluded by any of those will not receive it even if it matches the segment.
4. Keep the SDK up to date. Older SDK builds may not report the tags or events your segment relies on. The current releases are iOS SDK 7.2.0 and Android SDK 6.10.0.
5. Test with a direct HWID send. If a direct send works and the segmented send does not, the problem is in the segment definition or in the data on the device, not in delivery.