Which version of Lightroom are you using and what is your OS?
Lightroom version: CC 2015.6 [ 1078672 ]
License: Creative Cloud
Operating system: Mac OS 10
Version: 10.11 
Application architecture: x64
Logical processor count: 8
Processor speed: 4.0 GHz
Built-in memory: 32,768.0 MB
Real memory available to Lightroom: 32,768.0 MB
Real memory used by Lightroom: 10,092.0 MB (30.7%)
Virtual memory used by Lightroom: 11,346.3 MB
Memory cache size: 9,370.0 MB
Maximum thread count used by Camera Raw: 8
Camera Raw SIMD optimization: SSE2,AVX,AVX2
Displays: 1) 5120x2880
AMD Radeon R9 M295X OpenGL Engine
Version: 4.1 ATI-1.42.11
Renderer: AMD Radeon R9 M295X OpenGL Engine
I only updated today.
1 person found this helpful
Is your graphics card driver up to date? (I don't know much about AMD GPUs). This seems like a graphics card issue. Have you tried disabling the GPU in Preferences > Performance? This doesn't seem like it would be necessary with your GPU but it would be interesting to see if that makes any difference.
Mike, graphics software is in the OS with Mac OSX so cannot be updated..
Keith, yes try disabling the Graphics under Preferences>Performance....
I run with the graphics disabled, I have never found it to be of any benefit.
Is this consistent or just a random image???
Have you tried rendering a 1:1 preview??
I have had the odd glitch with previews not behaving as expected and the issues would clear of their own accord....
I'm curious as someone reported a while back the opposite with images gaining +5 without any actions!!!