Wierd silhouette during motion

Hey guys im looking for someone how can tell me what with wierd silhouette is and how to get rid of it.
it only occours if something is in motion. i often see character dragging big transparent kind of trail behind them.

its nothing game related since i have the same thing apearing in engine on any project. but it starts to go on my nerves

Temporal Anti-Aliasing and / or motion blur. The former is in the project settings (see how FXAA works for you) and the latter is in the camera / post process volume - Motion Blur amount defaults to .5.

sadly its none of the above.
i tryed changing diffrent settings including going from TAA to FXAA.
habe a closer look. i made a short clip. this trail is fairly long and remains fairly long
here you can even see some kind of artefacts
and just for the sake of it

here you can see the main problem.
its like the character is some kind of “hot stone” leaving a disturbance in the air

Sadly, I’m not enough of a rendering wiz - a bit out of my depth. Sorry. Hope someone more knowledgeable can chip in.

anybody got a clue?

maybe someone how can adress me to the right place?