So, if you look in ~/.config/kwinrc, under the [Tiling] section, you can see that there are various subsection named [Tiling][<UUID>], which each has a different tiles setting.
What happens, I believe, is that the tiling functionality is storing different layouts for different screens, and its screen detection logic isn’t very sound… On my system, I’m moving my laptop between different docks with different external monitors, and even KScreen is having some hard time with that (though it has stabilized a lot in the last year) and I often have to reconfigure the screens when waking the laptop from sleep and connecting to the dock.
The tiling configuration suffers from a similar problem - in my case, I disconnected from the dock, suspended the laptop, then woke it up and connected back to the same dock. As a result the laptop’s built-in screen tiling layout remained the same, but the external monitor’s layout has reset. Looking in the configuration file I can see that it created a new entry with a default layout.
I’m not sure how tiling decides that there is a new screen - the identifiers it uses do not correlate to anything that I can find, including kscreen identifiers (which is what I’d expect it to use). They are UUIDv5 SHA1 based hashes - so they look to be designed for consistency, but I have no idea what they are hashing and that does not seem to work well for the purpose of consistency.
I suggest you open a ticket about this at https://bugs.kde.org . Link it here, please, so I can follow up as well.