Hello Panelsofsilence,
I have also started having problems with Unreal Engine 4.12.5 after updating to 10.11.6 from Yosemite 10.10.5.
May I ask you, how have you resolved your problem?
May I also ask which operating system are you using now and whether it is working fine with Unreal Engine 4.12.5?
Thank you in advance for your answer!