BTW, I tried to find a work-around and noticed that reducing the size in the capture module to, say, 3000 x 2000, avoids the crash and the FITs viewer shows the downloaded image. As long as I select the Card as the capture destination in the INDI control panel, full-sized images are kept on the card, so I can finish a sequence without the crash of Ekos.
Since a fit file sent from my D5300 with the full resolution (6016 x 4016) does not cause any crash, at least this size of fits will be downloaded to the FITs viewer on Windows.