What actually is happening here when the image is split like this?

[VenomXts]

I am shooting in 4k 60 fps auto settings on an air2. I totally understand why I see this if a see a bolt split in half (see whole bolt of lighting in two separate frames but split individually).

What's going on with this and how could I fix this? Any ideas?

 

[Meta4]

That's probably due to the camera using a rolling shutter.
To avoid the problem with a moving subject, you would need a camera with a shutter that exposes the whole scene at the same time

 

[sar104]

Agreed - that looks like a combination of rolling shutter and automatic exposure control. The scene became significantly brighter during the vertical scan, causing the gain to be reduced mid-frame.