A7iv Random ISO Fluctuations

[Gschiffverre]

I’m getting random white balance changes with astro photos.  Both images same settings, one frame taken right after the other F2.8 ISO 3200 20”. One image will be cooler blue tones and the next will be very green/yellow. Has anyone else had this issue? 

[FunWithCameras]

This is a guess, but with astro photography involving comparatively little light (ideally!), the white balance sensor has very little to work with, so something like a passing plane could throw off the measurement. I would recommend setting a fixed white balance at the start, or simply ignoring the auto white balance values and setting a white balance when processing.

[XKAES]

Those are all good points to consider -- basically what are the cameras settings?  Turn AUTO OFF and set things manually.

Another one to consider is NOISE reduction and LONG EXPOSURE CORRECTION.  I don't know what your camera offers, but mine has options for these.  These may be "correcting" your exposures differently -- and you don't even know it.