Slightly incorrect statement. Actually, it was Sierra. I forgot I updated earlier to Sierra.
My SD card works again perfectly under Windows 10 thanks to... Parralel for mac version 12.
As I could not access my SD card from Windows 10 using bootcamp, I decided to give another try to Parralel fro Mac and downloaded the free version for 14 days. Elected the Pro version and selected "Use Existing Bootcamp"
Parralel spent some 30 minutes "updating" my bootcamp. I tried Parralel again and was still not impressed: Lower graphic resolution (which I am sure could be addressed by tweaking the settings) and slower system. So I decided to shutdown Parralel and switch from Sierra to Windows 10. There the SD Card worked again: I think that part of the update made on the Bootcamp partition by Parralel may have somehow fixed my issues.
I note that under the [Windows 10] driver manager, the Apple card reader USB drive is now in a different location under "Disk Drives" and to see it does not require to check "view hidden files anymore" as is usually the issue when the SD card.
prior to that I had tried to fix the driver issue under Device Manager. Did not work. I had tried to download a driver from Realtek as some suggested. Did not work. I tried to reinstall the Bootcamp drivers. Did not work. Only this last step worked.
So to summarize, if you have an SD card that works under Sierra but not under Windows 10 via Bootcamp, try to install parallel for mac version 12 and select the Bootcamp partition.
The system will "update" your Bootcamp partition and it might fix your issue when you get back to Bootcamp under windows, as I did for me.