regex - Node.js + express + regex paths, on page refreshes node.js doesn't send a responce

Question

When using the following route:

app.get(/\/api\/core\/(c|humanities)/gi, function(req, res) {
  res.send("HI");
});

On the first page load I get the proper 'hi' response. But after a few page refreshes I'll get 404 errors stating:

Cannot GET /api/core/c

The regex is supposed to match /api/core/c and /api/core/humanities as well as be case insensitive.

Any ideas?