First of all, follow these steps:

  1. Make sure you have a strong and stable Internet connection.
  2. Make sure the game is connected to Facebook.
  3. Open game Settings and disconnect the game from Facebook. Then reboot your device, launch the game and reconnect to Facebook.

If your friends are still missing, try the following:

  1. Open your Facebook page in a browser.
  2. Go to Settings & Privacy → Settings → Apps and Websites.
  3. Tap View and Edit next to Mystery Matters and make sure that the friends list is shared.
  4. Reboot your device and re-launch the game.

If the app is marked as "Expired", it means that the game's permission to access your friends list is no longer active. Press View and Edit next to the game icon and then Renew. After that, relaunch Mystery Matters for the changes to take action.

If none of the above steps work, try deleting Mystery Matters from the Facebook app list. Doing so won't affect your game progress, so no worries!
1. Open your Facebook page in a browser.
2. Go to Settings & Privacy → Settings → Apps and Websites.
3. Press Remove next to Mystery Matters.
4. Reboot your device, launch the game and reconnect to Facebook in the game settings.

Here are the reasons why certain people can disappear from your friends' list:

  • You un-friended those players on Facebook or they un-friended you;
  • These players uninstalled the game or unlinked it from their Facebook accounts.
  • Their games lost access to their friends' lists on Facebook, so they disappeared.
  • You and the other player (players) have older or newer game version installed — please note that interaction is impossible in this case. You can check your game version by opening in-game Settings and tapping the "i" icon in the upper-left corner of the window.

If you noticed that only a specific player vanished from the list, make sure you're still friends with this player on Facebook and ask them to follow the tips from this article.