Same issue here. Space is unaccounted for and appears to be missing. Have restarted the phone, wiped the cache, and tried clearing up things. Do not wish to do a factory reset as that doesn't seem like a valid solution. Phone is barely used (maybe 15 min a day), a handful of small apps, no gaming or videos. All photos/media moved to SD card. Stock android, up to date (not rooted).|
Problem noticed a few days ago, when an 'Insufficient storage' notification appeared. I was one system update behind at the time, and applied the latest update following the notification to see if it made a difference - it did not.
An excellent product is quickly becoming unusable.
Screenshot of Device Storage