Here is one of 70 lights I took last night opened in ASIFitsView on my desktop computer. 
Looks great.
But when I take the 70 subs, or even 2 of them, and stack them in Deep Sky Stacker, I get an image that consists only of the upper left 25% of this image. The current series of subs was generated with my Canon, but I also see this with my ASI 183MC. This has been happening ever since I took some pictures with 2x2 binning on the ASI 183MC a few weeks ago.
The FITS Header looks like this.
SIMPLE = T / file does conform to FITS standard
BITPIX = 16 / number of bits per data pixel
NAXIS = 2 / number of data axes
NAXIS1 = 3906 / length of data axis 1
NAXIS2 = 2604 / length of data axis 2
EXTEND = T / FITS dataset may contain extensions
COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy
COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H
BZERO = 32768 / offset data range to that of unsigned short
BSCALE = 1 / default scaling factor
CREATOR = 'ZWO ASIAIR' / Capture software
XORGSUBF= 0 / Subframe X position in binned pixels
YORGSUBF= 0 / Subframe Y position in binned pixels
FOCALLEN= 600 / Focal length of telescope in mm
EGAIN = -1. / Electronic gain in e-/ADU
XBINNING= 1 / Camera X Bin
YBINNING= 1 / Camera Y Bin
CCDXBIN = 1 / Camera X Bin
CCDYBIN = 1 / Camera Y Bin
XPIXSZ = 5.69999980926514 / pixel size in microns (with binning)
YPIXSZ = 5.69999980926514 / pixel size in microns (with binning)
IMAGETYP= 'Light ' / Type of image
EXPOSURE= 300. / Exposure time in seconds
EXPTIME = 300. / Exposure time in seconds
CCD-TEMP= 13. / sensor temperature in C
RA = 13.532445 / Object Right Ascension in degrees
DEC = 56.7458 / Object Declination in degrees
DATE-OBS= '2020-10-29T03:05:40.402' / Image created time
INSTRUME= 'Canon EOS 1000D' / Camera model
BAYERPAT= 'RGGB ' / Bayer pattern
ISO = '1600 ' / ISO Value
TELESCOP= 'EQMod Mount' / Telescope name
END
