Hello
I don't think it's your constraints that change but the geometry of your sketch. When you change one rib, the others adjust accordingly.
e.g. In a right triangle, if I change the length of my hypotenuse then at least 1 of the other 2 sides will also be modified.
I advise you to fix your sketch well, in particular by indicating a constraint with your coordinate system. (For example, you can start your sketch directly on the center of the coordinate system so that the rest of the geometry will be automatically constrained in space)
You can see that the sketch is positioned on the coordinate system. You must fix your sketch in space for it to become valid (green). To do this, either set it to the coordinate system or you go to "constraints chosen in a dialog box" and choose "fix"
Hoping to have answered your question.
I confirm what Ludovic says, always constrain in relation to the origin, either in a corner or in the center of a line depending on the case to avoid re-creating a shot for example.
Without it, the sketch does what it wants, whether it's on Catia or SW or any other 3D software, is one of the 1st things you learn about this kind of software.