Local Publish produces small file

[old gray beard]

This problem arose between June 8 and June 11, 2021. I have been trying to fix it since with no success. As far as I can tell nothing in NoF 15 has changed and nothing on my PC has been changed. Here's the problem:

When I local publish a page of my website, the file shows a much smaller file size in Filezilla than the last time I published it. For example, after publishing a file that was 10.7KB on the website, it becomes 707 Bytes in my local publish directory (also in Filezilla). When I upload the file to the website and view it (in Firefox, Opera, Edge, or Chrome), the link to it doesn't work. I get an error page that says 404 error "Oops! Looks like the page is lost."

I'm working on a Win10 desktop (HP with 12MB memory and a 1 TB SSD).

Anybody recognize this problem?