There's some kind of a bug in Android 5 on Nexus 5. I was trying to backup everything last night and that was a painful experience. Basically, storage kept failing. Rebooting the device and reconnecting to my laptop would fix the problem momentarily. That was last night, and the backup was successful.
This morning, my Nexus 5 was acting sluggish. Then HERE Maps would not launch. Then the device said there is no SD card (WTF?). So I reboot and that wiped all app data.
All podcasts... gone.
All photos... gone.
All audiobooks... gone.
Offline maps for HERE Maps and TomTom... gone.
But every app is still installed.
No big loss; I had created a backup of everything last night. Anyways. I'm going to wipe the device and start fresh.