Looks reasonable.

Instead of extracting the push message ID yourself, you could just pass the bundle in:
https://github.com/aerogear/aerogear-android-push/blob/2.2.x/aerogear-android-push/src/main/java/org/jboss/aerogear/android/unifiedpush/metrics/UnifiedPushMetricsMessage.java#L26

Are you able to share the HTTP 500 response payload ?

As well as some info from the UPS server log in WildFly (or EAP) ?

I wonder if this crashes, perhaps the messageID is null ?
https://github.com/aerogear/aerogear-unifiedpush-server/blob/1.1.2.Final/jaxrs/src/main/java/org/jboss/aerogear/unifiedpush/rest/registry/installations/InstallationRegistrationEndpoint.java#L221