XCode Problem - Couldn't load settings from contents.xcplayground
This happens when you zip and unzip files and Mac turned some files into .xml file depend on your mac settings. The solution is:
right-click the "xxx.playground" file -> show package content, you will see the "contents.xcplayground" file. Right-cilck this file and go to "Get info". Now in file name and extension section, remove the .xml at last.

Do the same for "contents.xcworkspacedata" under the "playground.xcworkspace" workspace folder.