A quick reproducer can be our example here:
https://doc.qt.io/qt-6/qml-qtquick-viewtransition.html#view-transitions-a-simple-example
Upon space key being pressed, new item is fading in and gradually popped out.

The thing is that is one presses space key too quick (threshold is less than Animation duration I think), then one will see:

Basically, if new item pops out before previous item can finish its animation, previous item freezes and can never be in place.