Settings > Display v Advanced = Is Auto-rotate screen on or off?
Pull down the notifications tab and you can see the Screen orientation option. Change it from 'Portrait' to 'Auto-rotate'.
aware, that is the problem, not working.
Is anyone else having issues with the screen rotation toggle not working after the 8.1 update? If it appears to be working for most, will try a factory reset, but want to confirm it's not a bug first. Please let me know, thanks.