Problem Definition

When you have a board where the swimlanes is based on Stories, the only issues you will have beneath Stories are Sub-tasks (in most cases). Knowing that this issue type doesn't have the Epic Link field, the Show/hide epic labels button have no utility on that scenario, instead, it might cause so confusion, leading the user to think that it's a bug.

Suggested Solutions

Either create a pop up to inform that in that scenario the button will not provide that information or disable the button.