It has been reported that for push notifications, Campaign will display 100% sent but no push notifications make it to the recipients.
One of the reasons found for this is a misconfiguration on the pipelineD service where APNS is mapping to APNS_SANDBOX.
The issue was addressed in CAMP-37240 which required a configuration change to the pipelineD process.
Documented change to serverConf.xml:
topic endpoint="" name="mccs_push_notifications_feedback" pipelineName=""
consume endpoint="" group="$(INSTANCE_NAME)_new" pipelineName=""/
/topic