Totally speculative, but what if the propulsion system is something like an Alcubierre drive? Then the object isn't moving, just moving the spacetime around itself.
Of all the possibilities for UAPs, super magic propulsion drives are the among the least likely of a number of unlikely explanations.
Cameras are weird and lenses have a lot of weird properties. Autofocus and aperture adjustment add more weirdness. Image sensors have their own weird properties and behaviors. Cameras on stabilized gimbals on a moving aircraft compound all of those properties and effects. That's all on top of the unintuitive nature of looking at things in the sky which often lacks a helpful visual perspective.
So sensor artifacts and co fusing perspective is far far more likely than magic space warp drives.
Either the pilots are telling the truth or they're lying. Sensor artifacts are totally implausible in both cases.
Even for a trained pilot the reference-free venue that is the sky is a bit mind bending. Even something the size of an airliner looks like an indistinct pill from a few km away. Atmospheric ducting [0] can make a plane too distant to pick up on radar visible to the eye or an EO/FLIR sensor.
There's also the pesky habit of "eyewitness" accounts being absolutely terrible. Someone can claim to have "seen" an object while they only did so through their plane's cameras. They think they remember "seeing" the thing so that's their story.
https://youtu.be/ZBtMbBPzqHY?t=459
If you have more to say that you'd also want me to address, it better be directly relevant to the events described in this video.