I reset keyboard settings and now its instantly learning. I can't believe I've been missing out on this feature for so long! To all those who didn't do a fresh install. Check this feature is working.
I tested by typing "My name is xxx" several times in notes and then typing "My" and watching it complete the sentence.
Think I was having the same issue too! Have been using it since before release and it never learned anything..Just reset the keyboard settings and now it seems to be learning!!! Thanks!