On Wayland panels set to "windows can cover" currently have their screen edge created on login and it works, but once it's activated one time it's gone and is never re-created.
What I've done (with fitting changes to KWin and plasma-workspace) is basically use the panelAutoHideHideCallback for both actual auto hide panels and for those that are only set to "windows can cover". I've tested it and this actually fixes the problem properly and makes the panel work like on X.
In order to make this a proper solution IMO either the function has to be renamed to fit the added purpose or of course a new one created. I'm not sure which would be better, if there'd be any compatibility problems when changing the name in the plasma-shell protocol or something like that. Some help on what to do would be greatly appreciated :)