The Testimonial Highlights widget is designed to showcase different sections of a single testimonial as individual highlights.
How the widget works
When you see the same user's picture appearing multiple times in your Testimonial Highlights widget, this is the intended behavior. The widget breaks down a single testimonial into separate highlight sections, which means one user can appear multiple times if their testimonial contains multiple highlighted portions.

Workaround for unique users only
If you prefer to show only one entry per user, you can duplicate the testimonial and remove some highlights from the new version. This gives you more control over which highlights appear in your widget.
Request a feature
If you'd like the ability to select specific highlights instead of showing all highlights from a testimonial, you can submit this as a feature request at https://feedback.senja.io.