External monitor keeps turning on mirroring

[KwanMan]

Everytime I plug in my external monitor, mirroring is turned on and its messes up the resolutions so I have to go into settings and change everything back. It wasn't doing this until a few days ago, before it would just automatically set it up as a extended display. Am I missing some settings to make the default option as an extended display instead of mirrored?

 

[mwhq]

In the display settings - arrangement, make sure in the bottom corner 'mirror displays' is unticked.