When you have a sketch on front plane and you hide it. You then start a new sketch on the front plane, why the first sketch that I hide before show up in the new sketch.

I like to keep all my sketch on the origin. So I can hide and use on other projects.

There can only be one sketch per plane. If you start sketching on the same plane as another sketch, it will become part of the existing sketch. If you want separate sketches, you’ll need separate offset planes.

What the Bum said. Also if you don’t select a plane or reference to sketch on, it can default to the original sketch I think. Sometimes I find lines in the middle of nowhere too, so there is that.

I thought each model have it own sketch, so you can hide it and start a new sketch for a new model.

For example each part in the train model should have it own sketch that you can hide. It doesn’t matter which plane you are sketching on.

In Shapr3D, sketches are completely disassociated with the model once the solidification function (extrude, revolve, etc.) is performed. There’s no such thing as a model’s sketch.