I ran into a bit of a problem with those files. I could download them... but then Windows was unable to rename, move, or even delete them. Investigation with the "file locksmith" feature of PowerToys revealed that Windows Explorer itself was locking the files.
After a while, I figured out the problem. I installed a tool (DarkThumbs) which will make thumbnail images of the epub covers (and a few other file formats too). It was attempting to create the thumbnails but essentially hanging. It works as a plug-in for Explorer, so it looked like Explorer was the one hanging.
I restarted Explorer and, instead of reopening the folder where the troublesome files was, I bypassed Explorer by opening a command-line (Terminal) and renaming the files from .epub to .zip (Epubs are actually zip files with a different file extension and particular rules to how the content should be organized-- many modern file formats are like that, such as the MS-Office and LibreOffice documents). That took care of the DarkThumbs issue.
Then I opened the zip files to figure out what was wrong. And it was not difficult to see: instead of the internal files residing at the root of the zip, they were all inside a subfolder. *That's not how an epub is supposed to be*. Some epub programs may be able to figure it out, but I wouldn't be surprised if others will get confused or just list the file as "corrupted."
Well, I repacked the files in the correct manner, renamed them to .epub and voilá... now they work as they should. I'm attaching the fixed files below.