Having an Issue with Character Select showing wrong Character for an instant.

Yeah, the same behavior occurs with variable changes set to run when the timeline starts on a slide. When a slide transition is applied, Storyline evaluates default states and variable values during the transition. Only after the transition completes do the slide’s triggers begin executing.

For example, apply any slide transition and increase its duration to around 10 seconds. Reference a variable that is initially set to False and add a trigger to change it to True when the timeline starts. Preview the slide and open the inspection tool, and you’ll notice that the slide-transition-container receives a transitioning class, which is removed once the transition ends. That’s the point when the slide’s actions and triggers actually begin executing. During the transition, the variable remains False; it only changes to True once the transition is complete.