LockDown Browser Keeps Closing on Mac - Permanent Fixes (2026)

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LDB launching then auto-closing within 5-15 seconds on Mac is almost always one of three things: a Gatekeeper rejection it didn't catch on first launch; a blacklisted process triggering an automatic abort; or a codesign verification failure. The fix is a clean reinstall + checking for blacklisted apps before relaunching.

Symptoms

Three root causes (in order of frequency)

  1. Blacklisted process detected (~46%) - LDB scans for blacklisted apps, finds one, shows the close dialog briefly, then aborts. The brief flash is too short to read.
  2. Gatekeeper rejection on second launch (~26%) - first launch worked, codesign cache invalidated since (often by macOS update), LDB now self-aborts on the failed verification.
  3. Codesign integrity check from inside LDB (~16%) - LDB performs its own signature verification on launch; if the .app bundle was modified post-install (e.g. by an over-aggressive antivirus quarantine), LDB exits.
  4. Other (12%): kernel extension conflicts, sandbox container damage, beta macOS issues.

Fix 1 - Identify and quit the blacklisted process

  1. Quit LDB.
  2. Open Activity Monitor.
  3. Click the "View" menu → "All Processes".
  4. Search for any of: VNC, ARDAgent, screensharingd, TeamViewer, AnyDesk, Citrix, Parallels, VMware, UTM, VirtualBox.
  5. Quit each (click the row → click (×) → Force Quit).
  6. Also check for Zoom-active, Teams-active, Discord-screen-sharing.
  7. Relaunch LDB.

The complete blacklist by default is in the conflicts cluster.

Fix 2 - Reinstall LDB

Resolves Gatekeeper and codesign integrity failures:

  1. Run the complete uninstall (uninstall cluster).
  2. Restart your Mac.
  3. Sign in to your LMS, download LDB fresh, reinstall.
  4. On first launch, approve every TCC dialog.

Fix 3 - Whitelist LDB in your antivirus

If you have Malwarebytes, Bitdefender, Sophos, or Norton, they may have flagged LDB's bundle as suspicious and modified it post-install. Whitelist:

Fix 4 - Disable Screen Sharing and Remote Management

System Settings → General → Sharing. Toggle off:

Each of these triggers ARDAgent or screensharingd to run, both blacklisted by LDB.

Fix 5 - Update macOS

System Settings → General → Software Update. Newer minor versions occasionally fix Gatekeeper rejection bugs.

If 1-5 don't fix it

Save the most recent ~/Library/Logs/DiagnosticReports/LockDown Browser-*.ips. Open a Respondus support ticket via support.respondus.com; attach the .ips and your macOS version. The crash signature lets Respondus reproduce.

Frequently asked questions

I quit every blacklisted process I can find but LDB still closes. What now?

The blacklist also includes daemons that aren't visible in Activity Monitor by default (until you click "View" → "All Processes"). Run that search first. Otherwise the cause is more likely Gatekeeper/codesign - Fix 2 reinstall.

Why does LDB close silently instead of showing the "Close these applications" dialog?

The dialog flashes briefly (sometimes <1 second) before the auto-close. On Macs with very fast displays the flash is hard to perceive. Fix 1 (manually checking blacklist) is the same procedure as if you saw the dialog.

Could my own institution's configuration be killing LDB?

Yes. The Respondus Dashboard lets your university customise the blacklist. Some institutions add productivity apps (Notion, Obsidian, Anki) that aren't on Respondus's default list. Check your university's LDB IT page for the exact blacklist.