According to Wikipedia Experience Design is
An emerging discipline, experience design draws from many other disciplines including cognitive psychology and perceptual psychology,linguistics, cognitive science, architecture and environmental design, haptics, hazard analysis, product design, theatre, information design, information architecture, ethnography, brand strategy, interaction design,service design, storytelling, heuristics, technical communication and design thinking.
While it is still a relatively new and emerging discipline, it has its roots in psychology, design thinking and various forms of user research. Given this background, people playing such a role are often in a dilemma of where do they fit in , when it comes to a fast paced lifecycle of an agile project.
If not resolved early, it is easy for user exerience designers to start working in a silo with minimal interactiion with the delivery team. This is counter productive as then the UX people have no idea of the project rythm and cadence and often end up taking huge amounts of time to deliver the relevant artifacts (wireframes, visual designs, content etc...) for the project.
This can become very frustrating for both parties and the best way to resolve this is by integrating the experience design people as a part of the entire project delivery team. Having a Lean approach towards UX leads to designers showing their work at regular intervals to the team, validating it and adapting , just like a regular agile lifecycle.
What works best during the course of a project is to have the UXers also accountable for each user story just like analysts, developers and testers. If you have more than one UXers in your team, ask them to signup as a UX Owner for user stories. This means that they are responsible for taking the user story or the feature all through to production from an experience design standpoint
Accountability to a user story is quite important because it integrates the work the UXers are doing to the daily cadence of the project team which is entirely based on user stories. Based on this, a typical standup update for a UXer would be something like this
An experience designer needs to work in a similar cadence as a business analyst who is trying to get the next set of stories analyzed for development.
A lot of small UI tweaks can be fixed very quickly if the UXers were to pair with developers and testers when they are actually integrating the visual design into the application.
So rather than working in a silo, a user experience designer has to be fully integrated with the development team during the entire project lifecycle. They carry the same responsibility as others in the team to maintain the flow of stories through till they are released.