If you use a duration of 0 for position animations in ListView/GridView remove transitions, the delegates will be out of place and overlap with each other. It seems like the bug may affect other transitions too, but I'm only able to see it with the remove transition using itemviewmodelandtransitiontest.qml. It also seems like any instant remove transition can cause the bug, even this:

remove: Transition {}

Most of the time you probably won't want a duration of 0, but KDE Plasma allows users to set global animation duration to 0 as an accessibility feature. The issue was first reported by a user here: https://bugs.kde.org/show_bug.cgi?id=483962

If you run itemviewmodelandtransitiontest.qml and filter the model using the text field, you should be able to see the bug yourself.

I have also attached a more minimal test file, minimal_itemviewmodelandtransitiontest.qml