solution that worked for me...
yes, you're right. it says win 8 but is recently updated.
went thru the hoops with this yesterday, including downloading new drivers. none of it worked.
lots of ppl trying different things. issue seems to go back to 2012. basically the rotation lock vanishes from the action center.
however, for anyone who may have same issue, what worked for me in the end was this -
(If rotation lock icon is missing)
Change to portrait mode in display settings.
Restart.
Screen comes back in landscape mode with rotation lock visible, and rotation is working again.
remains to be seen how long it will last!
not convinced now that it was an update. it's been going on too long for one recent update to be the cause. it's just plain glitchy, since win8