Misbehaving apps

I have an app, BBC news, that intermittently freezes my rooted nexus 5 running 5.1.1. It never did that when I was on kitkat. Just like when I was on kitkat I have several security apps (xprivacy, etc) running in the background.

How do I troubleshoot to see what is happening when the phone freezes and I cannot exit BBC app till I reboot?

Thank you.

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