Display arrangement keeps changing My iMac keeps changing the arrangement of my two add-on displays. The third one, the one in the middle, is the computer itself which always stays in the middle. 

I'm running High Sierra 10.13.6. It's a mild annoyance, but still annoying nevertheless. 

All three monitors have the dock and menu bar. Apparently no one else is having this problem because I cannot find a fix anywhere.

How can I ensure that the way I arrange my displays does not change?
I wrote a free terminal tool called displayplacer that lets describe your monitor layout as a terminal command. I then use BetterTouchTool to execute these profiles via hotkeys. I have the same issue as you, when I plug in my monitors the layout randomly changes.

For example, on my 4 monitor setup at home I have this profile: displayplacer "id:A46D2F5E-487B-CC69-C588-ECFD519016E5 res:3840x2160 hz:60 color_depth:8 scaling:off origin:(0,0) degree:0" "id:F466F621-B5FA-04A0-0800-CFA6C258DECD res:1440x900 color_depth:4 scaling:on origin:(-1440,1437) degree:0" "id:4C405A05-8798-553B-3550-F93E7A7722BB res:1440x2560 color_depth:8 scaling:off origin:(3840,-363) degree:270" "id:18173D22-3EC6-E735-EEB4-B003BF681F30 res:1920x1200 color_depth:8 scaling:off origin:(960,-1200) degree:0"

Also available via Homebrew brew tap jakehilborn/jakehilborn &amp;&amp; brew install displayplacer