I unchecked the checkbox in the Inspector next to a Panel’s name, expecting that this would hide the entire panel. This appears to work in Edit Mode, with the panel and all contents disappearing. But I enter Play Mode and at least one element rendered, a row of data instantiated from a prefab containing various text elements.
Another bug is that after it has been rendered on-screen during Play Mode, that row is visible again in Edit Mode; one of several instances I’ve found with the new UI where layout changes leak out across modes.