I have two notification widgets added to a separate panel each. Only one of the notification widgets will receive notification updates. I would expect them to stay in sync with each other.
Does the history contain all notifications? There is only one set of popups.
No, one widget remains entirely empty, the other one will get all the notifications. Usually the one in latte-dock, it seems.
You can't have notification widgets in separate processes. Either all in plasmashell or all in Latte Dock.
How am I supposed to know that as a user? I find it rather limiting, but if that's the case, the user should probably be warned here.