My crude but effective solution is a 7-line script. Whenever the dreaded dialog appears, the script presses Alt-A for "do this for all", and Alt-Y for "yes, lose the properties."
If you can bear the risk of downloading an .exe file, you can skip steps 1 to 3 and download the .exe at http://www.filedropper.com/stop-copy-dialog, and add it to your Startup Folder (step 4 below). ...but there have been a lot of bad programs hiding as AutoITscripts, so it's safer to take 10 minutes and compile it yourself. It's free and not terribly hard:
1. Download and install AutoITScript from autoitscript.com. (It's free and widely trusted alternative to VBScript. I used it because I've found VBScript unreliable in detecting Windows dialogs that are rapidly appearing/disappearing and modal, inactive, minimized, or otherwise odd. And, AutoIT is absurdly easy to compile to a standalone .exe, which I like.)
2. From the Github repository (https://github.com/joshwhitk/suppress-property-loss-dialog-during-copy-in-Windows-Explorer), save only the script file "stop-copy-dialog.au3" to your desktop. Open it in any text editor and read it carefully. When you're convinced it's harmless, rename it if you like and continue.
3. On your desktop, right-click this .au3 file. and choose "compile script (x86)" from the context menu (AutoIT added these). An .exe file (e.g "stop-copy-dialog.exe") will be created on your desktop. (You can uninstall AutoIT and delete the .au3 file now.)
4. Move this .exe file to your Startup folder (where? press Win-R to run shell:startup)
Run it, or reboot, and you're done! It runs in the background forever. When this (or any AutoITS script) is running, you'll see a new icon in your tray. It's a small white tab with a green square on the left.
Obviously, this script is a crude workaround. I would LOVE IT if someone figured out how to suppress those dialogs in the first place!
Please update Github with a text note if you do know of a better way (ie a registry setting): https://github.com/joshwhitk/suppress-property-loss-dialog-during-copy-in-Windows-Explorer
Oakland, California 94611