Trying to make a TextLabel's text the LocalPlayer's Rank in the group. Isn't working?

You can't do game.Players.PlayerAdded in localscripts. I suggest you making a RemoteEvent and call it "PlayerGroup" and put it in ReplicatedStorage.

Here is the the script you need to make in ServerScriptService:

rp = game:GetService("ReplicatedStorage")
playergroup = rp:WaitForChild("PlayerGroup")


game.Players.PlayerAdded:Connect(function(plr)
    local roleplr = plr:GetRoleInGroup(3336691)
    print(plr, "is", roleplr) -- This is useful for testing
    playergroup:FireAllClients(plr, roleplr)
end)

And this your localscript:

local text1 = script.Parent
local rp = game:GetService("ReplicatedStorage")
local playergroup = rp:WaitForChild("PlayerGroup")
player = game.Players.LocalPlayer


playergroup.OnClientEvent:connect(function(plr, rank)
    if plr ~= nil and plr.Name == player.Name then
        text1.Text = rank
    end
end)