I'm having quite the interesting issue on HS 10.13 PB3 - Fresh install in APFS with identical setup and minor changes to config.plist in different version of Clover (4128 on HS vs. 4035 on Sierra) will only boot with RX 480 to one screen. My completely working installation on 10.12.6 loads both screens no problem. IORegistryExplorer shows both connections in Sierra and only one in High Sierra using the same framebuffer (Dayman, the default I guess) but on different connectors. I'm using skylake with iMac17,1 SMBIOS with Lilu, WhateverGreen, and IntelGraphicsFixup for video output. Has anyone else run into this issue or would know how to troubleshoot it?