It is possible that you did not give Coin Master permission to access your Facebook friends’ list. Sometimes these permissions are revoked after an update and must be re-approved. Please follow these instructions on either a computer or mobile device:
Computer:

1. Log onto Facebook.
2. Click the drop-down arrow near the Home button on the upper right area of the screen, then select Settings.
3. Select Apps on the left sidebar.
4. Hover your mouse over the Coin Master application and click on the X button, then click Remove.
5. Restart Coin Master on your device and login to Facebook again. When asked to provide permissions this time, make sure you provide your friends’ list by clicking on Edit This and make sure there is a check-mark next to Friends list.

Mobile:

1. Open the Facebook application and click on the menu button.
2. Scroll down and click on Account Settings
3. Scroll down and press on Apps
4. Click on the first option Logged in with Facebook
5. Scroll down and click on Coin Master
6. At the bottom of this page press on Remove App
7. Press Remove
8. Restart Coin Master on your device and login to Facebook again. When asked to provide permissions this time, make sure you provide your friends’ list by clicking on Edit This and make sure there is a check-mark next to Friends list.