Hi wpigoury,
The call looks ok to me, and if it's working in your brower then it should be fine. Perhaps the issue isn't with the call, but rather the display of the content? Are you able to share a snippet of your code showing how you're assigning and iterating through the response?
Here's quick sample I tested that should work for what you're trying to do:
<#assign leaderBoard = rest("/kudos/authors/leaderboard?max_age=all&page_size=5").users />
<ul>
<#list leaderBoard.user as kudoUser>
<li>${kudoUser.login} - ${kudoUser.mixin.kudos.weight}</li>
</#list>
</ul>