I'm having a very similar problem. Just bought an (old) second hand CP-2500, completely new to the game so have no idea what to do in situations like this.
What's happening:
Cuts consistently don't start and finish at the same point, makes weeding very difficult. I've tried adjusting the blade offset, switched sign programs to no avail. Blade seems ok, swivels, nothing stuck in it etc.
Unfortunately it only came with a single blade and roll of vinyl so I can't really swap anything out to see if it's the problem, and don't really have any idea if it would be anyway..
Any ideas?