Fix run amok Mediaserver on Android that's depleting data quota and battery

clear cache

We're sorry to hear that you're experiencing problems with your data usage on your Nexus 5 device after updating to the latest Android version.

Troubleshooting for Nexus 5
To try and resolve the issue at hand, I have some troubleshooting steps I would like you to try:
Conduct a forced shut off by holding Power button and shutting phone down and restarting the device
Then, try clearing the cache partition. Here's how:
Hold power button for 2 seconds and select 'Power Off'
Press and hold the Volume Up and the Volume Down and Power keys at the same time for about 10 seconds.
An image of an Android lying on its back will appear.
Press the Volume Down key twice until "Recovery mode" appears on the screen.
Press the Power key to restart in "Recovery mode."
An image of an Android with a red triangle will appear.
While holding down the Power key, tap the Volume Up key.
The Android System Recovery screen will appear. Release all keys.
Use the Volume keys to scroll to wipe data cache partition and press the Power key to select.
The phone will restart.