My Asus Zenpad Z300M had been giving me problems the last couple of months after a system update. I would get com.process.media has stopped working errors on reboot, gmail and the play store would crash constantly, downloads and screenshots would fail, updates were always pending and I would get low storage error messages. I had to delete apps to gain space though I have plenty of storage.
After waiting for a new system update that never came, I was close to doing a factory reset. I then figured out that the system media storage app was using over 7GB of storage. To clear it, go to Settings->Apps and click on the 3 vertical dots in the upper right corner (more options) and select Show System. Scroll down and select Media Storage and then Clear Data. You can clear the cache as well.