Update (28 October 2021) : we now consider this case solved. See our Report of Investigation.
On 19 January 2021, at about 18:09 EST, we were shooting an International Space Station pass and experimenting with Direct Manual Focus (DMF) on the Sony A7 III mirrorless camera. The lens was a Tamron 28-75mm f/2.8 – a very good quality lens. The standard lens hood was attached, and video was captured at 4K resolution, 30 frames per second. We were looking to the East (you can see the constellation of Taurus in much of the clip). For a few seconds, a reddish, extended object “flew” through the frame, and was dismissed at the time as a lens flare. However, examination of the footage shows that is not a lens flare, so we’re baffled as to what it could be.
What do you think it could be?