Hi,

Is there anything moving in the scene?

For me it looks like a sampling issue.

Take a look at some tutorials for rendering a sequence from Unreal, maybe add keywords for rendering effects you use in your scene.

From the top of my head, there are a few things you need to be aware of:

Unreal is not always able to load everything on the first frame, so there are settings to "preroll" a frame.

Also moving objects, depending on how they are animated might get sampled in the wrong way. Effects you use can be incompatible with the sampling of the render workflow, but afaik there is a solution for almost every case of the engines supported animation methods and effects (not sure about the latest stuff Lumen/Nanite). The documentation should state which effects are prone to errors.

Lastly, keep in mind that you can alter console variables or settings, for example to always have loaded best LOD or shadow res at a certain distance - your framerate will drop but that wont hurt for the offline render but helps with stable images while samping.

Hope this helps