unmarked the solution to so this doesn’t auto close 
Thanks!
Now I’m back to being stumped.
I did replicate the issue on one website, so it’s definitely not something you did. In the previous version, the class name in the ExtUserSchema was userData. Since MyExtUserSchema (which is used to create the class and map files) is a copy of that, and CE doesn’t change that during upgrades, I assumed that it carried over and caused that to be the class name in the class map file.
I changed the class name in the latest version to conform to the PSR 1 standard. Since CE updates the snippet property to UserData during the upgrade to the latest version, that would have caused the problem. (Assuming that you upgraded from the previous version).
If my theory were correct, you should still have userData in your MyExtUserSchema chunk. You don’t, but then I don’t see how you ended up with userData in your map file, since CE re-creates all the class and map files whenever you submit the CE form, unless you changed the MyExtUser chunk after you submitted the form (which seems unlikely).
So, it’s still a mystery.
@halftrainedharry – you’re a better detective than I am, so if you have a theory, I’d love to hear it.