That's Cargolux, the Luxembourgeois (yes, that's the actual adjective) flag carrier airline.
From the picture of the mystery flight, it seems like tracking signal was lost and the plane was simulated by flightradar to be continuing flying straight in its previous path.
It's pretty common, especially around the Black Sea. You often see planes supposedly fly into Ukraine for example. The Caucasus - Central Asia corridor has also become very crowded due to western airlines' refusal to use Russian air space for Asian travel.
Any mystery deliveries would probably happen with military planes, without transponders on. And definitely not with a western company.