Machine: 5.3.0-51-generic #44~18.04.2-Ubuntu SMP Thu Apr 23 14:27:18 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Two weeks ago:
Installed the version from the web as described here: http://www.sweethome3d.com/support/forum/viewthread_thread,10146#47738
Installed the version from snap store by:
$ snap install sweethome3d
Or via the software centre (do not recall).
Both versions seem to work very slow, with the computer running to a halt even after the simplest of designs.
I then installed the version from the repository: 6.1.2+dfsg-1~18.04.1
$ sudo apt-get install sweethome3d
And this out of date version seems to work fine.
I would have expected the new versions to work better.
Please prefer to use official versions avalaible at https://sourceforge.net/projects/sweethome3d/files/SweetHome3D/