Visited state still shows hover effect – how to fix?

As Judy mentioned, this is typical behavior, and there’s nothing that needs fixing here. However, you can override this behavior by simply creating an additional trigger:

Example:

In this basic setup, note that the Hover state initially appears as a light blue color, while the Visited state is green. When we click a button, we see that the Hover state changes to a light green color, which is inherited and adjusted from the Visited state. What we don't see, however, is that Storyline, by default, creates many other states that are not visible or accessible to us. One of these states is simply a combination or mix of other states. For example: _default_Visited, _default_Visited_Disabled, _default_Down_Visited, _default_Hover_Visited, _default_Hover_Visited_Disabled, and so on. And this is exactly what we're seeing here. When we click a button, two states are applied at the same time: _default_Hover_Visited and _default_Visited.

Now, it's up to you whether you want to override this default behavior. It’s certainly possible to do so.