The device sends an empty GetChanges container, without any value. This is not supported in Z-Push (and potentially wrong IMHO).
Z-Push could workaround and see it as <GetChanges/>, that indicates that changes should be sent.
User-agent: 'AirWatch Boxer (Apple iPad; iOS 11.1) Version 4.8.1/1818'
Other versions sent a correct GetChanges and work as expected.
Reported in KS-39355