Raspistill returns a black image althogh preview is fine

Question

I am using Raspberry pi 3b+ with raspivam v2

raspistill -t 5000 -awb off -ex off -drc off -ss 5400 -awbg 1.1,1.95 -ISO 120 -ag 1 -dg 1 -vf -hf -o LastImageName.jpg

and get a good preview and a black file.

when I remove the -ex off I get an over exposed image. any ideas?

possible copy of Camera / raspistill - output image is black although preview worked - answer there did not work