This is a note about the cause and solution when file downloads in Google Chrome on Windows mysteriously fail.
Downloads from JavaScript, user scripts, extensions, and even normal downloads from SourceForge all became impossible.
Suspected causes: Chrome extension issues - this is almost impossible. It could be a Chrome settings problem, or possibly a behavior change in Windows’ standard antivirus software due to Windows updates.
Additional notes: I confirmed that downloads work with the same Google user account in Chrome on a different PC. Also, downloads work in Firefox. The same issue occurs even in incognito mode without extensions.
Solution: I restarted Chrome, but it didn’t resolve the issue, so I deleted Chrome’s history and cache, then restarted Windows. This finally resolved the issue.