There's a feature that prevents anyone using the 'Find A Player' tool from locating you. To activate it, follow these steps from the lobby screen:
If you're on a mobile device:
Keep in mind your friends will be unable to find you while this feature is activated. To turn it off, simply repeat the steps above to remove the checkmark next to the 'Hide from Search' option (desktop) or tap to deactivate the 'Remove Player From Search' option (mobile).