Board Thread:Current Major Glitch Discussion/@comment-30567431-20170519174359/@comment-27642721-20170522121624

The green checkmarks are records in the file MyHelpsForFriends.xml within the Social folder. For those with access to their files (root on Android/iOS and in all cases on Windows), deleting this file clears the checkmarks. A new file is created just as soon as you visit the next friend, so there's no harm done. Normally some game timer clears out this file from time to time, but it's independent of whether or not a friend has actually played the locations you've checked.