As there are multiple places where a local action can be listed, its possible you have the same local action listed in two of them. Below are the locations I'm aware of (though there might be others) that you might want to check:
-On the Case type (though you already noted you don't see it there). I believe there are case wide local action options, as well as local action options for smaller scopes within a case.
-As a flow wide local action on the flow's design tab.
-As a local action within the assignment shape.
Additionally, I recall that it used to be possible to have two flow actions that have different names, but have the same label. If you launch each local action from the list, one at a time, you can use the Live UI tool to check, and then review the locations I noted above to see if those rules are listed.