Even if the in-game overlay is not correctly displaying, we can still track your games to power your personal statistics in your profile page.
Here are a few alternatives on how to fix it:
Windows Aero must be enabled in order for in-game overlay to show.
Follow the instructions here to turn it on.
Go to Settings → Colors → Ensure “Transparency Effects” are turned on (this only applies to Windows 10 users).
Make sure all graphic card drivers are up-to-date.
If that doesn't solve, please send an email to firstname.lastname@example.org and we'll investigate.