Why can't I play a different action?

I’m trying to fix an imported fbx file with animations that aren’t working properly. While I can see the different actions if I open the drop down in the action editor, selecting a different action is not causing it to play - even when I scrub the time cursor into the frames where it should be animating. No matter what action I select, only the initial idle animation is playing. I thought that there might be something in the NLA editor which is overriding the playback, but I don’t see anything blocking it.

What might stop me from playing different actions, and how can I fix it?

This is the file:
troll_bug.zip (2.2 MB)

Look in the NLA. The top strip there is what is happening.

How do I fix that?

Delete it or mute it. Or add the rest and get them in the right priority (at the top) at the right time…