This creates an anonymous XYPanel, but doesn’t attach it to the current form, so it won’t be displayed. And without a lasting reference to that object, Python will discard it.
I suspect you should be referring to your form’s existing XYPanel:
An XYPanel is probably not what you want here. With an XYPanel, your code takes full responsibility for placing everything in that XYPanel, i.e., everything that has the XYPanel as its direct parent. And as you’ve found out, once placed in that container, a component is not going to move automatically, even if its neighbors are [un]hidden.
Whereas, if your container is a LinearPanel or ColumnPanel, instead of an XYPanel, then Anvil takes responsibility for closing up the space, automatically, when one of its components is [un]hidden. This is a feature I use frequently in my GUIs.