Autocad Education 2017 problem: "parasitic" traits that intersect

Hello

Here's the problem we're having with Autodad 2017 Education:

When opening the DWG files that we have, an error message appears on the screen (see attached photo) with "parasitic" lines that cross (in the background of the photo) that cannot be erased.

When printing or  using another version, the strokes do not appear.

 

Do you know if this is an option to be unchecked somewhere?

 

Thank you in advance for your clarifications.


probleme_autocad.jpg