I think I might have stumbled onto how to possibly reproduce it - it just happened to me in the orbiter while I was changing loadouts and forma'ing my guns. Rarely, when I exit the arsenal, I get this 0,5-1s hitch, or freeze - and that's the moment it happened, moved to the middle of my screen.
This micro-freeze happens very often when you join a match and begin loading into a mission, which might explain why it moves during that time. (Strangely though, despite Railjack missions having a much more pronounced "hitch" while loading in, it hasn't happened to me there yet.)
Next time I'll try to have shadowplay actually turned on and record it, if it happens in the orbiter again.