This has been an ongoing issue. The last version that works properly is v10.7.3.
I have three screens, one of them is my MBP's screen, I have a 27" 5K monitor directly above, and a 19" to the left. Every version after 10.7.3 results in only ONE of my screens being utilized and it is done at a very low resolution.
I have 'Use all monitors' and 'Optimize for retina displays' enabled. This works perfectly fine for 10.7.3 and older versions.
It's broken in every version after that, I have to keep a backup of 10.7.3 so I can restore it every time I test a new version.
Please see my post regarding previous versions: