The Cause: If the browser crashed or failed to load 20 tabs and only showed 1, and you then closed the browser, the browser "saved" that 1-tab window as the new "Previous Session," effectively overwriting the record of the other 19.
   The Fix: You should immediately check History > Recently Closed or use the shortcut Ctrl + Shift + T (Windows) or Cmd + Shift + T (Mac) repeatedly to see if the missing tabs are tucked away in a "Closed Window" entry. 

   The Cause: If you have an old phone or an old laptop gathering dust that still has an old version of your history/bookmarks, that device might be syncing "empty" data over your current data.
   The Fix: You should try logging out of your browser account on all devices, then log back in only on your primary machine to see if the deletion stops. 

   The Cause: Third-party apps like CCleaner, CleanMyMac, or even some Antivirus suites have "Privacy" features that automatically wipe browser data on a schedule. If the software is set to "Clean on Close," it will delete history every time you exit.
   The Fix: You should check if you have any system-optimization software running and disable "Browser Cleaning" or "Privacy Protection" for your specific browser. 

   The Fix: The most reliable long-term solution is to create a new Browser Profile. You can move your important data to the new profile and see if the "self-cleaning" behavior stops. 

That sounds incredibly frustrating. Losing tabs and bookmarks feels like losing "digital memory." Based on the behavior described—especially the part where the browser only "remembers" the one tab that successfully loaded—it sounds like a session file corruption or a sync conflict. Here is a breakdown of why this happens and what you can do to fix it: 1. The "Session Overwrite" Trap This is likely why the tabs disappeared today. Most browsers save the "Previous Session" based on the last window closed. The Cause: If the browser crashed or failed to load 20 tabs and only showed 1, and you then closed the browser, the browser "saved" that 1-tab window as the new "Previous Session," effectively overwriting the record of the other 19. The Fix: You should immediately check History > Recently Closed or use the shortcut Ctrl + Shift + T (Windows) or Cmd + Shift + T (Mac) repeatedly to see if the missing tabs are tucked away in a "Closed Window" entry. 2. Browser Sync Conflicts If you are signed into a browser account (Google, Firefox, or iCloud), the "deletions" might actually be Sync Overwrites. The Cause: If you have an old phone or an old laptop gathering dust that still has an old version of your history/bookmarks, that device might be syncing "empty" data over your current data. The Fix: You should try logging out of your browser account on all devices, then log back in only on your primary machine to see if the deletion stops. 3. "Cleaning" Software Interference This is a very common "hidden" culprit. The Cause: Third-party apps like CCleaner, CleanMyMac, or even some Antivirus suites have "Privacy" features that automatically wipe browser data on a schedule. If the software is set to "Clean on Close," it will delete history every time you exit. The Fix: You should check if you have any system-optimization software running and disable "Browser Cleaning" or "Privacy Protection" for your specific browser. 4. Profile Corruption If bookmarks are disappearing randomly, the local "Profile" folder on your computer might be corrupted or have "Read Only" permissions. The Fix: The most reliable long-term solution is to create a new Browser Profile. You can move your important data to the new profile and see if the "self-cleaning" behavior stops. Matt