Our advice right now is to not update your Nexus 9 to the Android 5.0.2 software as there are some serious issues going on right now.
According to Google’s product forums those updating to the latest software are breaking their devices and some slates have managed to become bricked in the process.
One user opened a thread in the Google forum’s after bricking the Nexus 9 with responses from the Google’s experts suggesting the best way would be to perform a factory reset in recovery mode.
Don’t do it
Some are also reporting the update is failing to install with results varying for each user, but most are reporting a simple restart will solve that problem.
We’ve reached out to Google for some comment on the situation but we haven’t had any response just yet.
Until we hear anything we’re recommending you just hold fire with the update until all the problems are ironed out.