When you start watching a recording that is in-progress, after fast-forwarding/skipping forward around 5 minutes, the scrubber will jump to the end and display a large number of minutes. However, you can continue to FF/skip ahead. So, from the recording's perspective, it knows where you are in the show, but from the scrubber perspective, it thinks you're at the end and if you back out, Channels will mark the recording as having been watched.
Also of note, this appears to happen on both Apple TV and Android TV. It also appears similar to this old forum posting: Often cannot resume where I left off while watching a recording in progress
Here's an example...
I submitted diags after the above happened:
Android TV - a35d957b-ed82-4fd0-b52a-f4cb77de251b
Server - a89b9dbc-8bf4-42e0-b2d1-1600d976bfb6
*note - the diags are from different times
Thanks!
