On a RX 5600 XT, OpenCore boots when connected by DisplayPort, but not when connected by HDMI

I'm in the process of modernizing an old Hackintosh setup, within the limits of the hardware at least. Here are my specs:

• MB: Asus P8Z77-I Deluxe
• CPU: i5 3570K (Ivy Bridge)
• RAM: 16 GB of DDR3 @ 1333 MHz
• GPU: Sapphire RX 5600 XT (Navi 10)
• SSD: Samsung 870 EVO 1TB
• HDD: Western Digital WD40EZRZ 4TB

I've got an OpenCore USB Monterey installer, created following the Dortania guide. I'm using a MacPro6,1 SMBIOS, per the guide. In fact the only settings I've changed from the guide recommendations for an Ivy Bridge desktop are the ones related to my GPU (i.e. adding RadeonSensor.kext, SMCRadeonGPU.kext and the agdpmod=pikera boot argument).

When I connect the machine to my monitor with a DisplayPort cable, OpenCore boots to the picker and then the macOS installer as expected. Here's a log from a successful DisplayPort boot: https://www.dropbox.com/scl/fi/lhiwiain03wleufn7wosi/opencore-2024-02-19-215525-DP-SUCCESS.txt?rlkey=fyr445f53ywao1tbyusqrzvop&dl=0

When I connect the machine to my monitor with an HDMI cable, one of two things happens. Sometimes, the machine gets stuck on the debug info that shows before loading the picker. Here's a log from when that happens: https://www.dropbox.com/scl/fi/9bp6ss9211y6ys5jyhmh0/opencore-2024-02-19-220342-HDMI-CRASH2.txt?rlkey=mgmaa9ocbrs67v5clgmh029ci&dl=0

About half the time, it makes it to the same pre-picker debug info, but then the screen goes blank. Here's a log from when that happens: https://www.dropbox.com/scl/fi/auukod8b73jpwz8w0ef92/opencore-2024-02-19-220230-HDMI-CRASH1.txt?rlkey=7gpwi8neq7jfdqufh94ogb7po&dl=0

If I boot it all the way to the installer when connected via DisplayPort, and then connect an HDMI cable, it recognizes it fine as a secondary display. If I then disconnect the DisplayPort cable, it switches to the HDMI as the primary monitor with no problems. So the ports, cables and display all seem to be functioning normally.

Interestingly, if I boot with both DisplayPort and HDMI cables connected, it boots totally fine, defaulting to DisplayPort as the primary display. HDMI shows up as a secondary display once the installer has booted. Here's what the log looks like in that case: https://www.dropbox.com/scl/fi/wty939jve1a4epdyfahff/opencore-2024-02-19-222918-BOTH-SUCCESS.txt?rlkey=0ubdd4f9mfjdlglhe7wrg1ijp&dl=0

If it matters, the display in question is a BenQ PD27705U, so a native 4K (3840x2160) resolution.

Any idea what might be going on here and how I might be able to get it to boot with only HDMI connected?

EDIT: If it's helpful, here's my config.plist: https://www.dropbox.com/scl/fi/xmkez3hu05vxe4fj5ug0q/config.plist?rlkey=zm43b4xh8ralm61bnwc66ucch&dl=0