I found a tether in a cave. When moving it back closer to my own tethers to use it, it connected at a high, close to vertical angle, through the cave wall. When I dropped the tether it showed no oxygen hose, but did provide me with oxygen. It was close to other tethers I'd dropped, but I couldn't see it being connected to them, and didn't think the ones in the cave above were close enough to connect.
I've posted a video with this bug name to my profile.
https://account.xbox.com/en-au/Profile?GamerTag=WizardSleeve555