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I have a preferred map seed that I have been using for a long time. I keep the original Autosave0 file from when it started back in February last year (2021), so just over a year ago. I have used it for three or four run throughs, typically starting soon after the release of each DLC. The last time was a game that I completed in December 2021 (I've been taking a bit of a rest from the game), which I probably started around September last year. One of the reasons that I use this seed is that I know the worlds well, and can concentrate on trying to see how the new DLCs impact the game.
Up until now, each time that I have started from that Autosave, I have got exactly the same islands with exactly the same recourses. However, this time it's different. The Old World is the same; same islands with the same resources. However, the New World is different. The islands appear to have the same outlines and the same rivers. However, the resources are different. This applies to the farming resources and also to Oil. Some islands that had oil now don't' and vice-versa.
Now, I accept that I now have a new challenge in that I get different farm resources from different places to bring to my production islands.
But, I always thought that starting from the same Autosave0 would give you exactly the same worlds. Indeed, I also though that using the same seed with the same NPCs would also give you the exact same worlds. Up till now this has always been true.
Has something happened, probably at GU13, 13.1, or 13.2, that deliberately changed the worlds, or is this a new bug that been introduced at GU13?
See examples:
Game from before GU13:
Game started 09 Mar 2022
As you can see, several farming resources have changed. Also, I have four extra Clay pits and 18 Oil Springs, which significantly affect the building space available (though saves me bringing oil to this island).
EDIT: Game files have been verified