You can debug the mobile app using any web debugger tool like charles or fiddler when you launch the app.
In the logs, you can find a demdex call (audience manager) that should have a registration token under of the variable.
ACS gets registration token from demdex call (https://dpm.demdex..net) so check whether demdex call is getting fired and it contains a registration token in a variable (d_cid) when the app is launched.
I see a demdex call with d_orgid and d_mid as parameters. The next message I see is the following: ID Service - IOException while sending request (Unable to resolve host "dpm.demdex.net": No address associated with hostname)