Syntorial won't keep my user

I installed Syntorial on my new Windows 11 installation. I copied the Documents/Syntorial folder from the backup of the old Windows 10 system, including my user.syn file.
When I loaded Syntorial, it didn't find my existing user and prompted me to create a new user. I did so then loaded my existing user using the menus and dialogues. My user loaded and progress updated from online.

But now, Syntorial never offers me my existing user on startup. Every time, I have to load the new empty one and then manually load mine, and every time it has to resolve the progress conflict because my progress is not saved locally. I lost all progress for a session that I finished offline.

Here's what's happening in the Documents/Syntorial folder: new users are created in a sub folder called 667cb87ed4cdb3ee0e1f2be2. When I load my existing user from Documents/Syntorial, it is recreated in that folder as well. However, every time I start Syntorial, it erases my user.syn file and keeps only the empty new user.

I've tried a number of things to try and work around this, but nothing works. I'm stuck with manually loading my user from the File menu and resolving the progress conflict every time. I'm unable to work though Syntorial offline.