iPhone XS is replacing iPhone 7 Plus, which used about 45 GB out of 128 GB. The migration was uneventful and everything seemed normal. Then I get "iPhone Storage Full" error. So I poke at Settings | General | iPhone Storage, and lo and behold, System at the bottom is taking more than 35 GB of storage. After Googling, I proceed to restore from backup, which brings it back down about 1 GB of System storage. Several hours later, it's back to 35 GB. What the heck is going on? At this point, I feel like making a Genius appointment. If they cannot fix it, I think I will demand a free upgrade to 256 GB.