There is a bug inside the article layout builder. If you create an article layout and set it as "default", then create another article layout and set THIS as default, you overwrite the old article layout. This also happens if you create more than one article layouts. Setting a (new) article layout (on a later time) as default, will overwrite the other (older) article layouts). I think, this should not happen. ;)

Tested on: Joomla 5.2.3, PHP 8.3.16 (Astroid 3.1.10)