I can now post more replies! This is material that was edited into an earlier message, now removed.
The image of the SD card is here: https://drive.google.com/open?id=1m167nKavhNmP42FpiqRgdzpuuGY7bczG and thank you very much.
This morning (U.S. Eastern time) I bootstrapped the Win 10 computer in Safe Mode with Networking and ran ten trials using Etcher Portable 1.5.57, all of which succeeded. I ran five more trials using Etcher 1.5.57 installed, and all of those succeeded as well.
I restarted the computer twice once to recover from the automatic start of apps after Safe Mode and again to get a cold start. Five trials of installed Etcher failed with checksum errors.
From that I conclude that either another process is writing to the SD adapter or Etcher’s output buffer is being somehow corrupted when Windows is in “normal” mode.
I still don’t understand why this problem appears only with the 09-26 version of Raspbian as released, and not with other versions of Raspbian, including the immediately previous version and even the 09-26 version after I’ve added some software and removed other software.
Software removed: Wolfram Mathematica and associated modules; Geany
Software added: Vivaldi browser, Gnome screenshot, w1thermsensor added to Python library.
Application launcher customized.