Preview ok but nothing in the captured images

AstroFlights

I am using ASI Studio 1.11.
Last night I tried to capture M57 with my ASI224MC attached to my 12" Dobson. I was happy to see the nebula in the preview and saved it, then I tried to save a series of 50 images, but all the ".fit" files contain no stars or nebulae. I repeated the process twice with the same result. What's wrong? Thanks for any suggestions.

Tech@ZWO

AstroFlights The fits file is the raw images, usually need to strecth the histogram to make the details visible.
You can click the histogram icon, then enable the auto button to try.

If the problem remains, pleas uplaod a fit file here, thanks.

AstroFlights

The histogram is very sharp, the auto button is enabled.
I tried to upload one of my .fit files, but the upload failed.
FYI The star size is 0.0, while in the preview file has normal values

Tech@ZWO

AstroFlights You can upload it to a cloud drive such as google drive, and then share the link here.