Hey @Dan Bar-Shalom40, let me first explain how and why it happened.
Let's say I earn 3 points for a like from last month, then early this month, someone unlikes my post. At this point we reduce the 3 points given to me and since my score for this month was 0, it'll result in -3.
Although, this is the designed behavior, you're totally right about the fact that users with negative reputation should not show up in the leaderboard. We'll fix this issue.