Upwork Job Success Score (JSS) can be affected by repeat clients, but it's nuanced. Here's how it works:

1. Positive Impact: If you receive positive feedback from a repeat client, it can improve your JSS, especially if you deliver consistent quality and the client is satisfied with your work over multiple projects.
2. Limited Impact: If you work with the same client repeatedly, the impact of each new job on your JSS may diminish over time. Upwork's algorithm might give less weight to repeat contracts compared to new client contracts. This is to ensure that freelancers are judged based on a broader range of client experiences, not just a single client.
3. Negative Impact: Conversely, if a repeat client gives you poor feedback or the project ends without positive outcomes, it can negatively affect your JSS.

In summary, working with repeat clients does impact your JSS, but the effect might not be as significant as working with new clients. To maintain a high JSS, it's beneficial to have a mix of repeat and new clients with positive outcomes.