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.