RX 580 outputs video to TV but not to monitor

[cat-holding-a-knife]

Okay, weird issue. My RX 580 outputs HDMI video to my TV just fine, but not to my KA242Y monitor.

I've tested every individual component and all of them seem to work just fine. Here was my test procedure:

TEST 1:
PC #1 w/ RX 580 > HDMI cable #1 > KA242Y monitor: Doesn't work. All fans spin up, but black screen on boot.

TEST 2: Removed RX 580, connected motherboard to monitor.
PC #1 w/o RX 580 > VGA cable > KA242Y monitor: Works. Boots to BIOS.

Test 3: Reinserted RX 580, connected video card to monitor, disconnected motherboard from monitor.
PC #1 w/ RX 580 > HDMI cable #1 > KA242Y monitor: Doesn't work. All fans spin up, but black screen on boot.

TEST 3: Plugged TV into PC using longer HDMI cable.
PC #1 w/ RX 580 > HDMI cable #2 > TV: Works. Boots to BIOS.

TEST 4: Plugged other PC into monitor.
PC #2 w/ RX 6650 XT > HDMI cable #1 > KA242Y monitor: Works. Boots to BIOS.

TEST 5: Plugged first PC into monitor.
PC #1 w/ RX 580 > HDMI cable #1 > KA242Y monitor: Doesn't work. All fans spin up, but black screen on boot.

I think I've isolated the issue to an interaction between the RX 580, HDMI cable, and monitor, but I have no idea what that could be. Any ideas?

 

[Caring1]

In GPU-z is UEFI checked?
What level HDMI cable are you using 2.0, 2.1 etc?
The issue is generally the communication codec in the cards Vbios.

 

[Vincero]

What resolution is the monitor?
Many older cards with UEFI GOP support are a bit broken when it comes to monitors with higher resolutions (usually when it's higher than 1080P). Some vendors have released fixes over time, but it's a bit more miss than hit in terms of that.

That said, this issue goes back more to the first generations of GOP cards of Kepler/Maxwell and GCN1 vintage, etc., when UEFI was starting to become a default for desktop PCs - an RX 580 using Polaris GCN4 really shouldn't have this issue.
What card manufacturer is it? Maybe they have a fix.

You could just work around the issue and connect VGA and HDMI to monitor - at least that way it will POST and show BIOS if you need it, whilst in Windows you can disable that output and use the HDMI instead... ghetto solution maybe but if its a case of using what you've got then not much choice.