This may not solve your specific issue, but just in case, I would still make sure you do not hide known extensions. To give you an example:

If you download userGuideExample.sh3d both IE and Edge (under Win10) will name the file:
[font=courier new]userGuideExample[1].sh3d .sh3l .sh3f .sh3t .sh3p[/font]
when downloading. Win8.1 keeps the original file name and does not create this mess.

Under Win10 SH3D opens the file, not as a plan (.sh3d) but as a plugin (.sh3p). SH3D puts the file in the plugin directory, reports successful plugin installation (SH3D does not open the plan or show the file in the plugin list - of course, it is not a plugin - the file just fills up [font=courier new]...\Application Data\eTeks\Sweet Home 3D\plugins[/font] with no meaning in life).

This gets even more confusing if known extensions are hidden (see Control Panel / Appearance and personalisation / File Explorer Options / View / Hide extensions for known file types). With hidden option on, the LAST of those extensions are concealed from the user. The actual .sh3d file, looks like a .sh3t file ([font=courier new]userGuideExample[1].sh3d .sh3l .sh3f .sh3t)[/font] and is treated like a .sh3p file.

I did see something about how Win10 has improved features in terms of sniffing out correct file types. I stopped reading, decided to go back to dual boot for my play PC, and not letting Win10 anywhere near a computer used for actual work.

ok