Sometimes, this block of code doesn't execute usually when there are more players in the game. What can I do to make sure it will work without skipping any player? Could the false parameter on TweenPosition cause it to skip?
for i,v in pairs(game.Players:GetChildren()) do
if (v.Character ~= nil) then
if v.Character:FindFirstChild("Health")~=nil then
wait()
v.Character.Health:Destroy()
game.Players[v.Name].PlayerGui.GameGui.Intermission:TweenPosition(UDim2.new(0.5, -50, 1, 0), "Out", "Linear", .3, false)
--game.Players[v.Name].PlayerGui.GameGui.Intermission.Visible = false
game.Players[v.Name].PlayerGui.LocalPlayerScripts.Intermission:Stop()
end
end
end

3 comments
The only reason I can see that it would error is because you call this before the player is done loading and something is nil. That or when when they join, the loop is already in process and they won't be added to the table.
It keeps happening all the time throughout the script. Like for instance, player's health doesn't get restored to 100, players dont get moved onto the map and other junk like that which should not happen
Make sure all of the GUI elements have loaded before you try to index them directly.