Finder icons without thumbnail preview and a cross?

Question

Today I imported (MacOS Catalina, 10.15.3) some RAW and JPG images from my Canon EOS R camera using ImageCapture. They are 3 CR3 bracketed (AEB) images and the JPG HDR created by the camera. Strangely, some icons are not visible in the Finder, and have a 'cross' on the upper left corner:

1. The images are there: all can be opened in Preview, and Adobe DNG converter may convert them to DNG. The view option "Show Icon Preview" is enabled
2. I tried to create a thumbnail using a newly created 'quick action' in Automator, and to drag that thumbnail to the icon shown in the 'Info' window for the IMR_0138.CR3 file; nothing happened. And, yes, I have write permission on the file.
3. This is not related to the file type: JPG files in other folders have their icon, and one out of 3 CR3 files here has its icon.

How can I have my files with their thumbnails displayed? Thank you in advance for any help!

Answer 1

Although it looks 99.9% complete, I think the Mac still thinks they are being copied over.
The 'thermometer' at the bottom of the icon would suggest this; the x at the top is so you can cancel before the operation is complete.

I'd try a reboot & see if that fixes it, otherwise try copy over again, maybe to a different folder.

If you were to look at them in List View, then the thermometer would be to the right of the file name, as either the same type of icon or as a 'pie chart', depending on version of macOS
Two views of a partially copied file, Icon & List.

^{These were done with Apple Remote Desktop, so the X is in that app's interface, not on the icon.}