Mine started a month ago too. I have been playing for years and had paid for the premium version. I have uninstalled and reinstalled the app multiple times. No friends list. I am very frustrated!
This just worked for me:
Close Scrabble. Open Facebook and logout. Close Facebook. Open Scrabble. Open Options and login to Facebook from Scrabble. Facebook will pop up and prompt you to login, then click Continue. Facebook friends list came back.