Root half of storage is gone on 16 GB model

[cad2blender]

I've had this nexus since release and never had problems with it. Currently it is rooted with the stock ROM and kernel. I noticed that I have so little space available...what gives? I'm using the 16 GB model, so I should be seeing about 12 GB available, not what is currently shown. I checked and deleted my twrp backups and I can't seem to find any files or folders that is taking up space, I even checked hidden folders and files. What do you guys think? I noticed today after recording some videos in 1080p and closing the app since it was out of storage space.
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[jmar]

You have to do a factory reset using standard recovery. It happened to me too.

Flash stock recovery, boot into fastboot and choose recovery. When you see the android on his back press power then volume up quickly in succession. This will bring up recovery option. Factory reset and wipe cache. Then power down. Then back into fastboot, and fastboot flash twrp recovery and flash your ROM again.