Are you using this joke when you are touring or just doing local showcases?

If touring, it might be a regional thing as opposed to the joke. For an example, I have more political jokes that kill in blue areas and

When I first started, I would do the same 5,10,15, which makes sense if you are touring because those people haven't heard the same jokes worked on until they're nice and cute. When you don't really venture outside your scene, people think "oh its gonna be the joke about the [xyz]". And if you know it's good, you probably use it in your sets more often than other jokes.

Also, if you, hopefully, have evolved as a writer, your material and tone will gradually change, so it may not currently match the tone, style, or quality of other jokes.

There's a lot of different things that could stop the joke from killing.

How I've tried to get out of that slump:

I will rearrange the order of my set so I don't feel like I am just saying it and instead actually getting into the joke.

Sometimes, I won't use it at all for like a month and force myself to think of a different joke, so when I go back to telling it, it feels fresh.