Multiple Monitor issue, connecting 3rd freezes 2nd monitor

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18 points

Multiple Monitor issue, connecting 3rd freezes 2nd monitor

So, I have had multiple monitors connected to my Macbook Pro M1 Max, running Sequoia 15.6.1, this has worked for years, but a few days ago after shutting down my macbook in sleepmode (also unplugging the poweroutlet of the monitors to save electricity before leaving the house for a few hours) it doesnt display my 3rd monitor anymore. If I hook my 3rd monitor up first (connected via HDMI directly into the Macbook) it works and gets recognized, but when I then add my second monitor (LG Dual UP) it freezes my 3rd monitor and it also gets removed from the Displays Settings. It is weird because MacOS recognizes the third monitor connecting since its adjusting the resolution for my second monitor, but it doesnt get any display after I connect after I have already connected my 2nd screen (LG Dual Up).

So, it used to work for a long time and now AGAIN it has happened. The first time I had solved it by chaning the Dual Up from its usbc connection to anotehr hdmi connection via a LINQ usb hub. This had solved that for a while for me but now the HDMI option is also not working anymore.

Problem is, whatever configuration i am trying with my usb-hubs, thunderbolt hubs, connecting usb-c or both HDMI, nothing seems to work anymore. Unplugging certain Anyone have any idea what the problem and solution could be?

MacBook Pro 16″

Posted on Aug 25, 2025 08:27 AM

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Answer 1

Aug 25, 2025 01:04 PM in response to hta48

if you have already met the cable length and specification requirements,

For MacOS 12 Monetary and some later versions, some users got relief by deleting two preferences files, then Restarting:

Library/Preferences/com.apple.windowserver

~/Library/Preferences/com.apple.windowserver.<UUID>.plist -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist

-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits

Restart REQUIRED after these deletions.

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Answer 2

Aug 25, 2025 09:07 AM in response to hta48

That LG Dual UP display, which appears to be model 28MQ780 appears to be a 2560 wide by 2800 (very tall for its width) single display with 10 bits/color HDR and 60 Hz refresh rate. there is no mention of supporting Display Stream Compression.

interfaces include:

1x DisplayPort 1.4

1x USB-C with 90 Watts power delivery

2x HDMI 2.0

At that resolution, and especially with HDR=ON, that display is very close to the limit of NOT being operable on standard cables at all.

For USB-C, You MUST limit is cable length to at most ONE meter of USB-C cable before being re-driven or converted. if converted to DisplayPort, the DisplayPort cable must be no longer than ONE meter maximum.

For HDMI, you MUST use certified PREMIUM or ULTRA HDMI cables of modest length.

You get a little more latitude if you turn HDR OFF.

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Answer 3

hta48 Author

Level 1

18 points

Aug 25, 2025 09:34 AM in response to Grant Bennet-Alder

Thanks for the response! So you would think this would be just over the limit on the Dual Up Screen. It just happened out of nowhere it seems. Why is it that it is now triggered? Well the other monitor is also LG (24 MR 400B) it is connected to the hdmi input but get rejected by my macbook atm.

How would you explain this happening? You think a certified Ultra HDMI could solve both these issues? The USB c is very short it comes paclkaged with the dual up as a connection option, so you would think that would suffice, this cable is not being converted to any other format but goes directly into my macbook.

With my macbook only sporting that hdmi 2.0 input would that even work with ULTRA or PREMIUM?

thanks!

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Answer 4

Aug 25, 2025 10:10 AM in response to hta48

HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

The cables "found" behind your TV set, and cables "Shipped in the box", are often 'lowest bidder' cables, and do not support the highest resolutions and refresh rates.

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Answer 5

hta48 Author

Level 1

18 points

Aug 25, 2025 11:06 AM in response to Grant Bennet-Alder

Ok understand! But I havent seen this is my issue as the cables I have do seem to work even though they aren't certified PREMIUM or ULTRA. This is basically my issue: MacBook Pro M4 Pro HDMI External Display … - Apple Community

I solved it using his method, so I think the culprit is some software issues

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Answer 6

hta48 Author

Level 1

18 points

Aug 25, 2025 09:38 AM in response to hta48

I have an app called BetterDisplay running to manage my displays might this be in conflict, since I have never had any issues with it and havent updated it in months I dont suspect it is cuasing it.

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