I'll be keeping my eye on this thread as I am also seeing this in our app. I have tried too many things to see what the route cause of the issue, but it does appear that the navigation structure is lost when multiple modal views are presented and the app is backgrounded.

I can confirm that this has been fixed as of iOS 26.1 Beta 2 👌.

I am also having a very similar issue when trying to focus the keyboard from the call back of a child view and was wondering if you managed to find a solution?