Hi @djhg,
I cannot see the problem looking at the gif you sent. It looks like you are activating the cut plane of “LevelB” and it’s working fine. If you need to change it in the Top viewport, then you need to make that viewport after first.
Please, could you send a video where I can see the problem in a clear way? I’ll probably need the file as well to be able to reproduce the problem in my computer.