22GB of my storage is filled but unaccounted for?

[Austin Stanley]

I have a OnePlus One on Android 6.0.1. / Cyanogen OS 13.1.1.

A large portion of my storage is taken up by stuff that I cannot find. I have 51.43 GB used, but 22.25 GB of that storage is unaccounted for. I don't have an SD card. Here is the breakdown in settings. I get the same numbers through storage analysis apps.

Apps - 6.91 GB
Images - 246 MB
Videos - 7.27 MB
Audio - 4.78 GB
Other - 16.17 GB
Cached Data - 1.96 GB

Total - 29.17 GB

However, I have 51.43GB used. What could be taking up so much storage, and how do I mitigate it?

 

[B. Diddy]

Use a file manager app to look through the user-accessible data directories, and see if there are any large .obb files that might have been left over from previously installed apps.