Different colors

Hi I’ve noticed that the colors result of the models is different using this plugin.

The same asb200.obj with an old plugin not available anymore on the old site:
https://cprgiunti.com/giunti/asb200-giunti-di-struttura-per-pavimenti/
and with 3D Viewer – 3D Model Viewer Plugin on the new site:
https://cprgiunti.altraforma.dev/giunti/asb200-giunti-di-struttura-per-pavimenti/

Look at the black on the sides that is missing in the second link, but using the same file.
How can I fix this behaviour?

Thank you in advance.

The page I need help with: [log in to see the link]