Intermittent magenta/black window artifacts on external monitor when “Disconnect built-in display” is enabled

[heungson]

MicrosoftTeams-video.mp4

When using mirroring virtual screen with HiDPI, screen on the external monitor occasionally shows severe graphical artifacts—magenta blocks across windows—whenever the cursor brushes the hidden macOS menu bar.

Steps to Reproduce:

1. Enable automatically hide menu bar option in mac os setting
2. Enable mirror virtual screen and HiDPI on better display
3. Connect an external monitor (USB-C or HDMI).
4. Move the pointer to the top edge so the macOS menu bar slides down.Expected Result:
   The menu bar appears and all windows redraw normally.

Actual Result:
Large magenta/black rectangles smear across window title bars, toolbars, and borders (see attached screenshot or video).
Toggle the built-in display on, then off sometimes clears the artifacts and do not reappear.
Disable HiDPI on BetterDisplay or BetterDisplay entirely removes artifacts immediately; they return once BetterDisplay is re-enabled.
macOS screen recording does not capture the corruption even while it is visible on the physical screen.

Environment:

• BetterDisplay version: 3.5.4
• macOS build: Sequoia 15.4.1
• Mac model: MacBook Pro 14-inch (M4 Pro)
• External display: Samsung G9 OLED 49 inch (5120 x 1440, mirror virtual screen enabled, HiDPI)

[waydabber]

Hmm. This seems to be some kind of macOS bug. If screen capture does not have it, then it's not in the framebuffer, the issue might be with the DCP or DCP firmware (this processes the framebuffer - video memory - and converts it to video signal). Issues like this can't be debugged really. Does this happen if you lower the refresh rate? If you are running the screen in high refresh rate, then the DCP might be at the edge of its pixel clock limit/processing power and might be failing somehow (just a theory).