A patient macOS user found the application which caused Sweet Home 3D to crash at the second step of furniture import wizard or in the materials modification dialog box.
It's BetterSnapTool and as soon as you stop this program, Sweet Home 3D doesn’t hang anymore. So if you use BetterSnapTool or a similar one like Magnet, Rectangle, Moom... disable them when you want to import a 3D model or modify materials.

Being able to reproduce this bug myself is going to help a lot to fix it. Meanwhile, I'll be happy to read if stopping these tools helped you too.