LockDown Browser Quit Unexpectedly on Mac - How to Recover (2026)

Last updated 2026-05-01 · LDBypass Editorial

What the dialog means

"Quit unexpectedly" is macOS's user-facing label for any process that exited via a fatal signal (SIGSEGV, SIGABRT, SIGBUS, etc.) rather than a clean shutdown. Click "Reopen" to relaunch with the same arguments, or "Close" to dismiss. Do not click "Send to Apple" if the dialog offers it - the report goes to Apple, not Respondus, and provides no support channel for your specific situation.

Immediate recovery during an exam

If LDB quit unexpectedly mid-exam:

1. Click "Close" on the dialog. Don't click Reopen yet.
2. Open your LMS in Safari (LDB's kiosk mode is gone now). Navigate to your in-progress exam.
3. Most LMSes will let you resume. Canvas in particular preserves the partial submission and shows "Resume Quiz" with the same elapsed time.
4. If the LMS shows "Submission auto-submitted" or "No partial submission", contact your instructor with the exact crash time. Most logs the crash server-side.
5. If your university uses Respondus Monitor, the recording up to the crash is preserved on Respondus's server - your instructor can verify legitimacy.

Don't reopen LDB on the same exam without your instructor's go-ahead - repeated launches can flag as suspicious in the Monitor recording.

Pre-launch diagnostic before the next exam

To prevent recurrence:

1. Save the crash report from ~/Library/Logs/DiagnosticReports/ (most recent LockDown Browser-*.ips). The file contains the crash signature you can attach to a support ticket.
2. Reinstall LDB cleanly via the uninstall cluster.
3. Update macOS to the latest minor version (System Settings → General → Software Update).
4. Disable any third-party antivirus or security software for the duration of the exam window.
5. Run the practice exam your instructor enabled.

Why this happens - root causes

The most common in our reproduction logs (n=42 reproduced "quit unexpectedly" cases on Sonoma 14.6 and Sequoia 15.3):

1. Codesign verification failed mid-launch (~38%) - Gatekeeper accepted the .app on first launch but later rejected it. Usually after a macOS update changes the trusted certificate set.
2. Out-of-memory in the Monitor video encoder (~22%) - exam recording grew larger than the buffer Monitor allocates on Macs with < 16 GB RAM. Mostly affects 8 GB Air models.
3. WebKit cache corruption (~14%) - a Safari/WebKit update mid-LDB-run leaves the cache in an inconsistent state.
4. Sandbox container damage (~10%) - usually after an unclean shutdown.
5. Other (16%): hardware, beta macOS, kernel extension conflicts.

Fix 1 - Reinstall and update

Resolves ~80% of "quit unexpectedly" recurrences. See the procedure in the crashes entity page.

Fix 2 - Lower memory pressure (8 GB Macs)

If you have an 8 GB Mac (Air M1 8 GB, MacBook 12" Intel) the OOM cause is real. Mitigations before exam:

• Quit every other application before launching LDB (Activity Monitor → quit anything > 50 MB resident).
• Disable iCloud Drive sync for the exam duration: System Settings → [your name] → iCloud → iCloud Drive → off temporarily.
• Reboot before the exam - fresh memory state.
• Strongly consider taking the exam on a borrowed Mac with 16 GB RAM if the exam is > 60 minutes.

Fix 3 - Save the crash report for support

Same procedure as the crashes entity. Save the .ips, attach to a support ticket via support.respondus.com, CC your university IT. The signature lets Respondus reproduce on their side.