Data Store: Infinite yield possible on...?

Hai. This is the script:

local playeractive = false
local statsDS = game:GetService("DataStoreService"):GetDataStore("StoreName")
local prefix = "usr_"

game.Players.PlayerAdded:Connect(function(plr)
    local points = plr:WaitForChild("Backpack").AvailablePoints
    local strength = plr:WaitForChild("Backpack").Strength
    -- load data in
    local data = statsDS:GetAsync(prefix .. tostring(plr.UserId))
    if data then
        print("Data loaded for " .. prefix .. tostring(plr.UserId))
        points.Value = data[1]
        strength.Value = data[2]
    end

    points.Parent = plr
    strength.Parent = plr 
end)

game.Players.PlayerRemoving:Connect(function(plr)
    local data = {
        plr.Backpack:WaitForChild("AvailablePoints").Value,
        plr.Backpack:WaitForChild("Strength").Value
    }
    -- pass a table to save
    statsDS:SetAsync(prefix .. tostring(plr.UserId), data)
end)

game:BindToClose(function()
	for _, plr in pairs(game:GetService("Players"):GetPlayers()) do
	    local data = {
	        plr.Backpack:WaitForChild("AvailablePoints").Value,
	        plr.Backpack:WaitForChild("Strength").Value
	    }
		print("Data save exit is ", unpack(data))
	    -- pass a table to save
	    statsDS:SetAsync(prefix .. tostring(plr.UserId), data)
	end
end)


local event = game.ReplicatedStorage.Erasure.RemoteEvent

event.OnServerEvent:Connect(function(plr)
          local data = {
        plr.Backpack:WaitForChild("AvailablePoints").Value,
        plr.Backpack:WaitForChild("Strength").Value
    }
    -- pass a table to save
    statsDS:SetAsync(prefix .. tostring(plr.UserId), data)
end)

My only problem is at line 46, and at every plr.Backpack:WaitForChild("X").

Once finished this, I'll finally be done with Data Storage, could you help me for the last time? (Or that is what I hope.)

ERROR:

Infinite yield possible on 'Players.Myname.Backpack:WaitForChild("AvailablePoints") Stack begin Script 'ServerScriptService', Line 46 Stack end

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