Скачать или смотреть Strange light phenomenon: reflection? drone? fighter jet? UFO (unknown flying object)?

strange light in the sky over Europe 2020-October-04.
The light was filmed by me but I have no explanation for it.
I guess it was a military aircraft but couldn't find any evidence.
For reference of speed: at 03:03 of the video there is to see an A320 at 39025ft, 462kts, with an approximate distance to me of 2 nm from me flying enrout from London to Warsaw (according to FR24).
The noise shortly thereafter is a train.

I highly doubt the theory of reflection, since I checked all my surrounding several times after I saw it for the first time (before I took the video it suddenly stopped from high speed and then decended or moved off rapidly) and all glass obstructions (window) were removed. Furthermore I think it was a (military) aircraft since it has standard aviation lights.