When you are switching to another layout, all objects from the current layout are destroyed. If the same objects exist on the new layout, their instances will be re-created, possibly with different UIDs.
You can set an object as Global, it will be transferred to other layouts. But you should be careful, it's very easy to mess things up with global objects. For example, if you switch to "eren" layout and then back to "main", you may end up with two instances of Eren object. In this game I wouldn't recommend it.
Ah, that makes sense actually. It's probably deleting the previous version of the object and replacing it with a new one, which is... honestly pretty frustrating, but interesting nonetheless.
Weirdly enough though, it only seems to do it to new objects. The "sling", "bronze" and "dalila" objects work perfectly fine, being Global just like "erin", using almost identical event sheets (only differences being the objects affected and the dialogue shown on screen).