[appledude]

It has to do with the 5K screen. Try This:
Quote:

Thank you for contacting Avid Technical Support. Currently there is a Quartz Redrawing issue with Pro Tools and 4k and 5k displays. This issue is being prioritized with our Engineering team and they are also in touch with Apple, to help resolve this issue as quickly as possible. Currently, here are the recommendations given by Engineering and Apple for better performance:

1) BUILT-IN RETINA DISPLAY SETTINGS:
-> Choose: sRGB IEC61966-2.1 (away from the default), found here:
System Preferences > Displays > Color > Display Profile

2) QUARTS REDRAWING ISSUE with 4 and 5K monitors:
-> iMac 5k models, as per Apple:
-> Set to 2K for it to be smoother

3) Try the following on iMacs particularly 5K models (As per Apple):
->Disable Automatic Brightness

I hope this helps as our customer was dead in the water with that issue and is now back to work done.