I think that you are correct in thinking it is in the female end that you are plugging into. If it works when you plug it into a different outlet than your string is working fine and must be a power issue. I am not very familiar with the Light Keeper Pro, but some of those type of testers get fooled when you have a bad connection on the neutral side. The power side might be connected so the tester thinks you have power, but your lights can’t work because the other slide of your plug(the neutral side) is not connecting.
Reputation over time
It looks like this user hasn't gained any reputation yet.
Once they have, you'll be able to view a graph of their reputation gained over time.
Here's a preview of what the graph will look like: