SC2 Mac Freezes, graphics?

My iMac Pro freezes when playing at high graphics setting reaching high demand, like when I’m winning with a full super army battle… Same iMac on Bootcamp doesn’t freeze at all at same graphics setting. I’ve tried both metal and open gl beta.

Hardware Overview:

Model Name: iMac Pro
Model Identifier: iMacPro1,1
Processor Name: 18-Core Intel Xeon W
Processor Speed: 2,3 GHz
Number of Processors: 1
Total Number of Cores: 18
L2 Cache (per Core): 1 MB
L3 Cache: 24,8 MB
Hyper-Threading Technology: Enabled
Memory: 128 GB
Boot ROM Version: 1037. (iBridge: 17.16.16065.0.0,0)
Serial Number (system): C02WV06YHX8F
Hardware UUID: 542549AA-C2BA-560C-B4C4-83639DF87F61
Activation Lock Status: Enabled

Radeon Pro Vega 64:

Chipset Model: Radeon Pro Vega 64
Type: GPU
Bus: PCIe
PCIe Lane Width: x16
VRAM (Total): 16 GB
Vendor: AMD (0x1002)
Device ID: 0x6860
Revision ID: 0x0000
ROM Revision: 113-D0500D-114
VBIOS Version: 113-D05001A1XT-018
Option ROM Version: 113-D05001A1XT-018
EFI Driver Version: 01.01.114
Metal: Supported, feature set macOS GPUFamily2 v1
Display Type: Built-In Retina LCD
Resolution: 5120 x 2880 Retina
Framebuffer Depth: 30-Bit Color (ARGB2101010)
Main Display: Yes
Mirror: Off
Online: Yes
Automatically Adjust Brightness: No
Connection Type: Internal