I don't mix anything. I do it the same way I've always done it (at least for almost all of my Android apps).
See here:
And as I said before, on iOS Screen1 cannot be closed, so there are always exactly 2 screens open at the same time after another screen from Screen1 is opened. Afterwards, all other non-Screen1 screens will be closed again as long as you do not return to Screen1. In the latter case, of course, only 1 screen (namely Screen1) is open.
So that's not the problem. Because as I already mentioned, switching between Screen1 and Screen3 works as often as you like without any problems. Switching between Screen1 and Screen3 doesn't work as often as you like, but leads to a crash after 4-5 attempts at the latest.
So there must be a problem with Screen2, even though it is identical to Screen3. By the way, I have now found the cause of this (after hours of trying). I would never have expected the result or thought it was possible as a cause.