After having serious issues after updating from iOS 10.3.3 like crashes, freezes and resprings I did a restore and deleted all contents, which fixed all my problems. Now they are back and it's worse than ever. It seems to me that the issue arises when I update from an older to a newer version. Something happened during that install. I'm sure if I restore my iPhone 6S again and set it up as a new device it will fix the issues. But I'm not doing that, it's time consuming.