Users are reporting black and splotchy like graphical issues in their projects when working on a Mac and using an AMD graphics card.
The user in the link provided mentions, "that UE 4.8.3 is without these errors on the same system. So I'm assuming it's happening only because some changes in 4.9."
I tested this issue on the Mac machine in the compat lab, which has an AMD Card, but was unable to reproduce the issue there. The card in the machine differs from the cards the users are reporting the issue on, so the test was not really valid. I have provided the hardware specifications of the Mac in the Compat lab in which I ran the test.
Hardware Specs of user reporting issue:
System is iMac late 2011, with Intel Core i7 / AMD Radeon HD 6970M 1024 MB
Another user reporting similar issue:
OS X 10.10.3 with Xcode 6.3.2. Computer has 2.3 GHz Core i7 CPU, 8 GB 1333 MHz DDR3 RAM, AMD Radeon HD 6750M GPU with 1 GB VRAM, and 128 GB SSD.
Head over to the existing Questions & Answers thread and let us know what's up.