This is all on the mobile site. I go to Account, type in a new username and save and the screen goes blank for ages and never reloads until I eventually refresh and my username doesn't change.
I've changed names quite a lot previously so thinking maybe I'd hit some sort of name change quota I tried reusing an old name but that didn't work either. I've encountered this issue every time I've tried for the past month. I really want some advice on a few issues I wish to keep private and some IRL people know this username.