When too many VPP apps are pushed as required apps, installation may fail. The logs will show the following error.
ErrorCode returned by Apple: {code=9632, reason='Too many recent calls to manage licenses with identical requests'}
The issue will occur if too many VPP apps are pushed. XenMobile server tries to associate license for all required VPP apps within a short period. This suggests that Apple is throttling the requests.
To solve this issue, reduce the number of required VPP apps by adding them as optional apps.