Very unexpected things happen, like items in a specific region in the App UI stop responding to clicks next time once you interact with them.
However I find it fine on iOS and the issues are usually around Apple changing something in the behaviour of the UI or API and breaking it, then you need to fix it for specific versions of the iOS. That's what you get when a framework is not mature yet, I guess.
That said, I don't think there's a turning back. It might be buggy but it definitely feels like the right way of building UI.
Oh, about the performance, you can build very sluggish or very responsive UI with SwiftUI because there's a night and day performance cost difference between "re-calculating and re-drawing" the UI and adjusting a property of it. Always try to structure your components in a way that changes happen by changing passed values instead of inserting or re-doing the views.
SwiftUI works quite a bit like React, many performance lessons from React will translate into SwiftUI.