External display freezes when a second display is added.

Question

Level 1

4 points

External display freezes when a second display is added.

Second external monitor freezes (2021 16" MBP with M1Pro).

I've been using my MacBook Pro with two external displays for years. Suddenly, I am running into a problem where when I connect either of my external displays, they work, but when I connect both, the one connected to the HDMI port becomes inaccessible.

The monitor continues to display what was on it, but when I move a window or my mouse across, it bypasses that monitor altogether, and when I go into the settings menu, it recognizes only the built-in display and one of the external displays.

I was running MacOS 26.1. I just updated to 26.2, but it didn't fix the problem. Also, I changed out the HDMI cable, with no results.

MacBook Pro 16″, macOS 26.2

Posted on Dec 12, 2025 2:35 PM

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Answer 1

Dec 13, 2025 9:57 AM in response to evetswal

AOC 24B1W appear to be a HD display 1920 by 1080 at 8 bits/color. refresh rates up to 76 Hz.

interfaces

HDMI 1.4

Analog VGA

Changing HDMI cables is a hedge against cable that are Broken, not against cable that are under spec.

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.

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BenQ GW2270 appear to be a HD display 1920 by 1080 at 8 bits/color refresh rates up to 76 Hz.

interfaces

Dual Link DVI 1.4 -- (a superset of ordinary Single-link DVI)

Analog VGA

Dual-Link DVI is only REQUIRED when the display is wider than 1920 wide. So in this case, a simple single-link DVI adapter or adapter/cable is all that should be needed for this display, and using a high-end expensive Dual-link DVI adapter is not needed, but should not have any bad effects.

This adapter/cable should have only ONE meter of cabling before the DVI converter, and can have (but generally does not have) up to one meter AFTER the converter.

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Answer 2

Dec 12, 2025 4:15 PM in response to evetswal

what make&model display(s) are connected?

how are they connected? just cables? adapters? docks?

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Answer 3

evetswal Author

Level 1

4 points

Dec 13, 2025 9:29 AM in response to Grant Bennet-Alder

I am using an AOC 24B1W monitor connected directly to the MBP's HDMI port, and a BenQ GW2270 that is connected to the laptop via a DVI to USB-C cable.

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