The stats of users on a course level won't be displayed if the user belong to a group.

To recreate the issue:

• Create a course
• Create some test users (in a way that you can connect with this account: manual login with a password that you can use later )
• Enrol users to this course
• Make sure that the users doesn't belong to any group
• Connect with one or more of the users
• Navigate through the previously created course with these test users (to create some stats data)
• Reconnect as an admin to this course
• in the participants tab, open one of the users that you have used previously
• click on the link "All logs" in the Reports area 
• Confirm that you have stats being displayed
• Go back to participants tab
• create a group
• Add your test user to the group
• Go back to the All logs report
• The stats doesn't show anymore and notice the message "Nothing to display"