I can't get my phone screen to auto horizontal though it's marked for it

[JMGalaxys8plus]

As of 03/25, I can't get my phone screen to automatically turn horizontal when I turn the phone though it is checked to do so. 

Did something happen with this last update?

[LaDawnyeay]

A lot happened with this last up date, not good either!!! So many nasty little annoying things!!! Some big annoying things!!

[HONEYBUNCH123]

Mine same thing. The phone constantly changing or rotating from portrait setting to horizontal. What is going on. Two weeks now l have this issue all day 24/7. How can it be corrected

[missmyflipphone]

Hold down the portrait button and it shows some new features. Fair warning it will cause extreme annoyance and the need for a punching bag

[Jameswalter]

Rebooting an Android phone is easy. To do so, press and hold down the Power button on your phone. Then, choose Restart from the menu that opens.

[Karkar22 · Accepted solution]

Ok actually this is a new feature, though not obvious. Where there used to be three options: portrait lock, swivel from portrait to horizontal depending on how the phone senses you are looking at it (auto rotate), and landscape lock.
Now there are two options: look and auto rotate (swivel). I believe the default mode is portrait. To get the phone to lock into horizontal view, do this...
Hit the lock button (where it says 'portrait, be sure it shows the auto rotate button.
Turn your phone sideways so it shows a horizontal or landscape view.
Hit the button again while in landscape( horizontal) view and it should lock into landscape view.
To change the options for auto rotate, hard press the button.