macOS Sierra can't detect 2560 x 1440 monitor resolution correctly

Using any version of 10.12.x on a Macbook Air 2013 13" my experience was that DisplayPort always worked (direct cable or with adapter) and HDMI (miniDP to HDMI) didn't work. I've seen many different permutations of success and failure while researching this problem. For me the ultimate solution was:

GitHub - Floris497/mac-pixel-clock-patch-V2

Don't forget to PayPal him a few $s if it works!

What are the optional resolutions listed at the bottom of the selection panel, below the 1600 x 900?

I think you should file a Bug report, as not supporting monitors that were OK before, is something that should get fixed

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feiguan wrote:

Hi BobHarris,

Thanks for the info. I've already filed the bug report. Bug28460128

Good. If you see anyone else having issues with their external monitors, encourage them to file as bug as well. The more problem reports, the more likely they will escalate a solution and get it into an update.

I have exactly the same issue with Acer G257HU Monitor.

On El Capitan I was able to run it with a 2560x1440 resolution (although only through a hdmi port on my 15'' rMBP, thunderbolt was a no-go). Right now I can't get it past 1080, SwitchResX doesn't help.

Sierra has however fixed a problem with a different monitor that I was using (Asus VH222), which I couldn't run on 1080 without help of SwitchResX, right now it's ok out of the box.

Anyways, the 1440 and other resolution problems including HiDPI scaling seem to be affecting numerous users following the public launch. I hope that Apple will address this issue swiftly.

Please file your own bug report. It is important that Apple know a lot of people care about using external monitors on their Macs

<https://discussions.apple.com/thread/7677753?answerId=30697964022#30697964022>

I also filed a bug for the same issue for my Acer G257HU, that now is giving me a headache with the 1080p resolution.

This low resolution is somehow also using up a lot of CPU/resources, and the temperatures of my MBPr (2012, 2.3Ghz/16GB Ram) are spiking despite being idle.

Is there any idea, in general, how long it will take before this is fixed?

If anyone would be told, it is the person or persons filing the bug. HOWEVER, software developers generally do not state something will be fixed by date X, because until the fix is out the door, anything can happen to a software release, and making a promise that does not happen is worse than saying nothing.

So chances are you will only know it is fixed when the software update is released that fixes it. And not before.

I'm having the same issue with my Acer K272HUL.

the highest resolution it can go since update is 1920x1200

I called apple support and they couldn't find anything. They elevated it to engineering but no ETA for a fix.

Im also having this issue with my mid 2012 MacBook pro (non-retina). Using El Capitan i was able to use my Asus VX279Q via thunderbolt to HDMI. Now since updating to Sierra it will not recognize the external monitor at all. As soon as I plug in the thunderbolt cable, the built in display just flickers every couple seconds.

I tried to call in for support but was advised that I should contact Asus to see if they intend to release any driver updates for sierra compatibility.

Darth_awesome wrote:

Im also having this issue with my mid 2012 MacBook pro (non-retina). Using El Capitan i was able to use my Asus VX279Q via thunderbolt to HDMI. Now since updating to Sierra it will not recognize the external monitor at all. As soon as I plug in the thunderbolt cable, the built in display just flickers every couple seconds.

I tried to call in for support but was advised that I should contact Asus to see if they intend to release any driver updates for sierra compatibility.

Please file your own bug report. It is important that Apple know a lot of people care about using external monitors on their Macs

<https://discussions.apple.com/thread/7677753?answerId=30697964022#30697964022>