No, I mean this page:
https://mangadex.org/settings
The cog in the menu bar works, but not the “more settings” page.
I’m making a guess to say that it could be due to the uploaded image. If I remember right, I had this problem in the username/profile pic settings page before, but not on the other pages. The default settings page worked too.
But I added a MD banner some time ago. And now it doesn’t save anymore.
On both these pages there’s a custom uploaded images (pfp and MD banner), and both were able to save before I added those images.
EDIT: and I am not sure if it is specific to IOS 11, it could be, as I have never been on mangadex with a PC before.