What I mean by stock system is just the installed OS, before you restore your data, and before you redownload the apps you had installed before. It is possible an app is causing the problem. Testing with just the stock software would rule that out.
It could be something is corrupted in the OS. That may explain why the security wipe didn't improve things. And maybe something got messed up with the upgrade. I really don't know. But I'm suggesting reinstalling the OS as you would on a BlackBerry handset after you've tried everything else. Take a look at the following link for the general idea.
Force your BlackBerry PlayBook to Update with Latest OS - N4BB
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