Launced from ShangriLa?
And the fact that its a plane is way more apparent once it stops making a contrail (which is due to it moving between two regions of air its colder and/or more humid out to sea than inland)
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A couple of days later a new photo of the trail was discovered from a known time, heading and position, this allowed the location of the trail to be triangulated, and it became apparent that UPS902 was a better fit than AWE808."
The video I linked above illustrates the match.