Facing the same issue since upgrading to iOS 18.2 on a full SwiftUI application I am building for a client. I have told them to not upgrade to iOS 18 for now since we have not been seeing this issue at all on iOS 17?! Bizarrely not just occurring for custom back buttons, but custom buttons also seem to intermittently show the issue, with the issue being most obvious when a .fullScreenCover is presented. I really hope Apple release a fix for this as this is a serious blocker on iOS 18!!!