So it seems like after update 1.10, me and some other users' positional tracking is no longer working when facing away from the sensor. Using webcams/phone cameras confirms that the LEDs on the back of the headset are still lit up. There's a topic on the Oculus subreddit (linked below) discussing this issue.
Not sure whether it's related, but one of the things in common with those who have the issue, is that we all opened the "First Contact" app in the tutorial section of our libraries. One of the users claimed that the tracking seemed fine until they open that app.
In my own limited testing, Mountain Goat Mountain doesn't seem to be affected by the tracking loss, but other apps are, including Oculus Home itself.https://www.reddit.com/r/oculus/comments/5chmes/positional_tracking_lost_facing_backwards_after/