Part of model disappear after scaling

I’m importing a stl model and when trying to resize it, one part of the model disappear after using the scale tool.

If you check the video below you can see that that later converts to something else during the operation.
Anyone have ideas on what is happening here?

Video:

Hi, please can you send the STL file to support@shapr3d.com. We would really like to understand what is happening with the design.