Hi Stas, thanks for the fast response.

The camera was set to NEF and I don't know how the setting of helicon remote looked like. I didn't control it.
The stack-files - about 40 - have been stored on the camera.
First 2 or three exposures were NEF and the rest JPG, low resolution.
I have no idea ...

I noticed a very bad mistake: the file type of my stack shots changed after a few exposures from RAW to JPG during one session.
I used a Nikon D800e and a MacBook 13" via USB. This never happened before.
The camera setting has been NEF/RAW as always. And this was to bee seen on camera display after ...