LockDown Browser Black or Blank Screen on Mac - 9 Causes Ranked

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A black or blank LDB window on Mac means the WebKit content layer failed to render, the Screen Recording permission isn't granted, or LDB is rendering to a different display than the one you're looking at. Force-quit, reset Screen Recording, disconnect external monitors, then relaunch - fixes ~75% of black-screen reports.

Symptoms

Causes ranked by frequency

  1. Screen Recording permission missing (~28%) - without it, LDB's kiosk-mode renderer falls back to a black surface.
  2. External monitor confusion (~18%) - LDB launched on a disconnected display you can't see.
  3. WebKit cache corruption (~14%) - usually after a Safari/WebKit update mid-LDB-run.
  4. GPU driver hiccup on Apple Silicon Macs sleeping then waking (~12%) - the discrete-GPU-equivalent rendering path.
  5. Hardware-accelerated WebKit disabled (~9%) - older Macs or specific accessibility settings.
  6. Display arrangement bug (~6%) - Display arrangement reordered while LDB was open.
  7. Dark Mode + dark exam content rendering invisibly (~5%) - rare LMS-side CSS bug.
  8. Magnifier/Zoom feature interference (~4%) - accessibility Zoom tracks LDB and stalls rendering.
  9. Other (4%): hardware-specific, beta macOS, third-party display utilities.

Fix 1 - Force-quit + reset Screen Recording (~52% success rate)

Same procedure as freezes. Force-quit LDB, remove from Screen Recording in System Settings, relaunch.

Fix 2 - Disconnect external monitors

If LDB is rendering on a disconnected/disabled display, you'll see a blank because the rendering surface doesn't exist on your visible display:

  1. Force-quit LDB.
  2. Unplug any HDMI, DisplayPort, or USB-C-to-display cables.
  3. Disable AirPlay (Control Center → Screen Mirroring → off).
  4. Disable Sidecar (System Settings → Displays → click the iPad → Disconnect).
  5. Confirm only the built-in display is active in System Settings → Displays.
  6. Relaunch LDB.

Fix 3 - Clear WebKit cache

rm -rf ~/Library/Caches/com.respondus.lockdownbrowser/
rm -rf ~/Library/WebKit/com.respondus.lockdownbrowser/

Fix 4 - Wake-from-sleep workaround

If the black screen happens specifically after waking your Mac from sleep with LDB open:

  1. Force-quit LDB.
  2. Lock your screen via Control Center → Lock Screen.
  3. Unlock with Touch ID / password.
  4. Relaunch LDB.

This re-initialises the GPU rendering pipeline. Avoid letting your Mac sleep during proctored exams; set System Settings → Battery → "Turn display off after" to "Never" before launching LDB.

Fix 5 - Disable accessibility Zoom and Magnifier

System Settings → Accessibility → Zoom → toggle off temporarily. Some Zoom modes track focused windows and stall LDB's render. Re-enable after the exam.

Fix 6 - Reinstall LDB

If 1-5 don't help, run the complete uninstall + reinstall procedure (uninstall cluster).

Frequently asked questions

My LDB shows a black screen but I can hear the audio prompt of the system check. What's happening?

This is the "WebKit failed to render but the AVFoundation pipeline started" combination - Cause #3 (WebKit cache corruption) or Cause #5 (hardware-accelerated WebKit disabled). Run Fix 3 first; if that fails, reinstall.

Black screen only on my external monitor - what now?

Cause #2: LDB launched on the built-in display but your focus is on the external. Either move the LDB window (you can drag it via the menu bar even when invisible) or disconnect the external and let LDB re-render on the only remaining display.

Is the black screen counted as cheating in the Monitor recording?

No. The recording captures whatever is on screen, including a blank LDB window. The instructor reviewing the recording sees the blank just like you do; it's clearly a technical failure, not an integrity event.