Hi, @Suet Mui
Thank you for posting in Microsoft Q&A forum.
We may start from checking the PolicyAgent.log in client to see if client get the policy, then check AppDiscovery.log, AppIntentEval.log, AppEnforce.log, etc.
Here is a great article has the troubleshooting steps, you may check it for more details:
https://deploymentparts.wordpress.com/2015/08/14/how-to-track-an-installation-through-client-log-files/
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