I have purchased several of these from Learning Resources https://www.learningresources.com/stem-robot-mouse, don't use them that often and now for the second time I have one that doesn't move in straight lines.  Its tracking is skewed to one side or the other.  LR replaced one, but now that I have a second faulty one, and the 1 year warranty is up, I have to pay (with a discount) for a replacement.  Am I just unlucky, or is this a common problem?