I'm seeing something similar in Tether. In my case there are two devices, "unknow" and "network device" that are reporting many terabytes of traffic, but looking at my ISP's usage reports this doesn't seem to be true--I don't have anywhere near that amount of traffic on the days in question.

Also, though I can't find "unknow" in the list of clients, that "network device" does show up with some inconsistent metrics. It shows high traffic downloaded/uploaded in the terabyte scale, but below that it reports "total traffic usage" under 3 MB.

It looks like a glitch in the firmware or app that is reporting a consistent (and very high) amount of traffic every hour for these two clients. This is happening with an Archer BE230 (firmware 1.0.4 build 20250519 rel.47087) and the Android Tether app (version 4.12.124).

Thanks @Joseph-TP, that's a good suggestion. I tested it using the Tether app on a different device (an iOS device, since I was testing with Android before) and I do see the same high traffic reported there. It started around midday on Jan 1 and continued until midnight yesterday, Jan 4. Then today that traffic disappeared, the "unknow" and the "network device" are still on the list but not reporting any significant traffic since midnight.

I have no idea what the "unknow" device is since it doesn't appear in the list of clients, but I figured out that the "network device" is a family member's iPhone--which wasn't even in the house for some of the periods of time when that traffic was being reported.

I'll go ahead and send those details to support, thanks for your help!