So I had this problem on my Iphone 6 - too much space taken up by Other.
I did take it to the Genuis Bar. They suggested backup, factory reset, restore from backup -- I did that twice (I used Itunes, not Icloud), with no effect / improvement.
I now have an Iphone XS with 256GB storage, less than 1.5 months old. It shows the same issue --right now its 50.7GB of System Usage (iphone) or 31GB (per Itunes).
And yes, I have tried all the steps suggested here as well as by members of the Genuis Bar on the new phone as well -- it does not work.
So its obvious, this is not a hardware issue - new iphone XS (plus a factory reset on the old iphone 6 cleared the problem on the old phone).
It certainly appears like this is a software problem -- and none of the suggested solutions fix it for me (and I am presuming for the many other posters on this thread).
Should I assume all of this is due to software corruption -- that is getting transferred from phone to phone via backup restore ?
And the only way to fix this is to do a factory restore without restore -- which means I lose a significant amount of content ?
Any thoughts ?