[BUG] Random surface generation

I am facing random surface generation while gently drawing lines on my sketch, any idea what is going on here?
For information, previous lines were drawn in this area before the bug, it seems that they still persist after their removal.



Can you download the model to your computer then attach it here for us to check.

It seems possible the old geometry was hidden not erased. As box wrote, if you share the model we can check for the cause.

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Just to show you what @slbaumgartner and I are both guessing, hidden edges can allow strange faces to form.

Hidden edges

It can also be due to incorrect usage of tags.

Some lines were indeed defined as “hidden geometry”. Are there any conditions for the lines to be set automatically hidden, or it is obligatorily a user condition?
Thank for those quick answers.

Edges may be auto hidden during a follow me or pushpull to create a smooth surface. But most of the time it requires explicit user action. In @Box s animation, the hidden rectangle would have to be done manually as there is no multi-face surface involved. Note that assigning a non-visible tag will also cause this.

This behavior is an example of why most experts recommend never to assign tags to edges or faces and to use the hidden flag only as a temporary measure.

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@matthieu.magnon, assigning tags is usually a manual thing. Do not assign any tag to raw geometry, leave them untagged.
However exploding tagged groups and components make their basic geometry (and all that was inside their environments) inherrit the group’s / component’s tag. So if that tag is invisible in a scene you’ll get yourself an “automated case of problems”.

Ok, thanks for those explanations