Joined: 20 Mar 2017
I am experiencing the same.
The only explanation I have that there is only limited amount of extreme sudoku "maps".
So when you run out, you get lesser level and so it's much easier.
That's just my opinion but it happened to me like a year ago, then I switched phone and it was hard as ever.
Few weeks ago after long time playing I encountered the same error on new phone too.
I recommend to uninstall the app and install it again. The cache will be removed and you start over.
Can someone from admins confirm or deny it?
Have a nice day,