iPhone 6s Storage issues

My iPhone 6s is showing inconsistent Space Used on iPhone Storage. Before updating to 15.0, my iPhone was nearly full of the 16G of storage space and now after the update, it shows around 1G Used with plenty of free space. I'll check it again and it will show less than 1G Used. Now I have over 3G of Apps, Music and Documents on this iPhone as well as the IOS of 6G. Then when I connect the iPhone to iTunes, it shows that the storage is full.

Now the iPhone is working just fine with apps and no problems updating or uploading to my iCloud etc. Just wondering if there is a fix to get accurate Storage Data reading.