I'm speculating here, but maybe Fastmail are deprecating this feature.
I do not use the feature, so it's not available for me.
You (DumbGuy) do use it, so it's still available for you, otherwise you would not be able to turn it off.
Or it's a bug.
Anyway, here's what I see:
https://drive.google.com/open?id=1xj...0nnmbKslsPgFRJ
Edited to add: the spam score still appears (automatically) in the subject of emails in the Spam folder. I see no change there.