Well, you can't blame T-Mobile for your Nexus 9 Google controls that OS 100%
If you're having crashes, it's most likely the app itself or in rarer cases, another app interfering (like one of those task killer things).
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I agree that this could be an app issue. Most of the time, if you just uninstall some 3rd party apps then give the phone a restart, it helps. If it's a preinstalled app that's problematic, clearing the cache and force stopping it can be helpful as well.