I have seen it several time, in my opinion, I think it’s due to 2 people joining in the same time, and got lucky to somehow both of them are getting in the server.
One time I seen 2 and 3 extra people in the server than the limit suggested.
If games require a specific amount which should not exceed the limit, a quick player count script should fix:
local Players = game:GetService("Players")
local PlayerLimit = 10
Players.PlayerAdded:Connect(function(player)
if #Players:GetPlayers() > PlayerLimit then
player:Kick("Sorry, this server is full.")
end
end)