Weird 4k Monitor issue

Hardware:

CPU: Intel Core i7

GPU: AMD Radeon RX 480 8GB

RAM: 32GB 2400Mhz DDR4

MOBO: Gigabyte z170X UD5 TH

WIFI: Apple Airport

BUILD: OC 0.7.1, MacOS Catalina

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Hey everyone, very weird monitor issue I've run into that I was hoping someone has seen before. I've been running a 3 monitor setup for a while, and recently picked up an Asus PA329CRV 4K monitor to replace two of the 1080p monitors in my setup. Strangely, when I boot the system both monitors display bios screen, but after OC bootpicker screen just the monitor still left from the old setup displays anything. The system boots fine, and even recognizes the new 4K monitor in system preferences, just doesn't show anything. Here's the weirder part: when I boot from my system backup clone (same exact ssd model but in an enclosure connected over USB), the new monitor displays just fine. It seems to be that booting from the M2 slot on the motherboard creates a conflict with just this monitor. I'm not sure if this is a hardware limitation of the mobo or an OC issue, was hoping someone could point me in the right direction. Like I said, I've been running a 3 monitor setup from the same GPU and booting from the M2 slot for years with no issues. Any ideas?

Much appreciated.