MacBook Air M5 only detects one external monitor after waking from sleep

awncana wrote:

Hi, my MB Air M5 refuses to work properly with 2 external monitors. I have done all the research, it seems it is a very common issue, but with no resolution, so I thought I would make my own post in case I am missing something. I have 2 Samsung OLEDs, one connected via DP, the other HDMI. I also tried both with HDMI.

The issue is that once the MB goes to sleep, it will only detect 1 monitor when it wakes. This was with the 2 monitors plugged directly into the MB. I have since picked up a UGreen TB4 Dock, and the results are exactly the same.

Apple says the M5 MBs are capable of supporting 2 external monitors so what am I doing wrong?

The only things I can think of:

(1) Cables are too long for the quality of HDMI you are utilizing. (Frankly, this seems unlikely.)

(2) You say Samsung OLED, but how are they configured? Apple specs for the 13" MacBook Air M5 say "Two displays up to a native resolution of 6K at 60Hz or 4K at 144Hz, One display up to a native resolution of 8K at 60Hz or 5K at 120Hz or 4K at 240Hz."

Are you exceeding those specs, e.g. resolution or speed? The reason I ask is that some Samsung OLED displays advertise much higher values for those parameters and might be configured by default to exceed what the Mac expects.

(3) Something is wrong with your MacBook Air. To rule this out you could make a Genius Bar appointment (or an appointment at an Apple Authorized Service Provider). Once at the appointment, they can connect two displays (most service providers have external displays connected to sample Macs on the premises or have them available in their shop) and you can test for the issue.

awncana wrote:

Thanks for the response. The cables are 6.6ft, I did also try 3.3ft HDMI only, no change. Both monitors are at 1920x1080 120hz, so thats not an issue. I guess #3 could be the problem, but I'm guessing with how many people online have posted this problem that it isn't an issue with my macbook specifically. The issue is however intermittent. Once in a while both monitors will come on.

Since you said it is intermittent, that still makes me focus more on the HDMI cables. It seems that you are using 1080p video in your set up, which should work with two monitors. I think that requires HDMI High Speed if not HDMI Premium. What are your HDMI cables rated for? When they are directly connected to the MBA, are you using an adaptor? If so, what is it rated for? (And I assume that your dock is rated for two such simultaneous video streams ...most are)

P.P.S. Some have found that deleting a preference file resolved their issue like yours:

External Monitor Not Detected After macOS… - Apple Community

This is an excerpt from the link I just sent you earlier.

P.S. You might find some useful information in this thread:

External Monitor Not Detected After macOS… - Apple Community

Although it is quite long. I suggest you read all of Grant Bennet-Adler's posts in that link about how to troubleshoot and address issues with multiple monitors not working properly, Grant is very knowledgable about this topic (much more so than I am).

The UGreen Revodok MAX 208 (on Green web site) indicates "Dual 4K@60Hz Display: Connect dual displays through Thunderbolt 4 for smoother multitasking and more screen space." It does not mention that two monitors with 1920x1080 would work with 120 Hz, however. It does say that one monitor @ 2K works with 144 Hz.

As for the Anker HDMI Cable, from what I can see here https://www.anker.com/uk/products/a87e0-anker-hdmi-cable-usbc-to-hdmi-cord?variant=57823413338486 it specifically mentions 60 Hz but not 120 Hz.

Technische Daten

Compatibility

Dell XPS 13, Dell XPS 15, Galaxy S23, Galaxy S24, MacBook Air, iPad Air, iPad Pro, macbook pro

Connector type

HDMI, USB Type C

Data Transfer Rate

60 Hz

Number of Pins

43

Maximum Voltage

10 Volts (DC)

Material

Nylon-Braided

Length

3 ft

I'm not criticizing your setup but I would suggest you focus on the cables/dock because the behaviors you describe sound more like a cable or dock issue that something with the Mac itself. And you said it is the HDMI one that is ignored.

Apple says ( How many displays can be connected to MacBook Air - Apple Support )

Two external displays

Supports two external displays in the following configuration:

Two displays up to a native resolution of 6K (6144 x 3456) at 60Hz or 4K (3840 x 2160) at 144Hz

You indicated both monitors are at 1920x1080 120Hz, I would think that would work but the above specifies 144Hz, should it also work at 120 Hz?

But as I said, I don't think it is the Mac that is the problem. Can you try running this stuff at 60 Hz (as a test)?