Why aren't the TweenGui methods working?

Ok, so I have a couple of GUI's in my place that rely on the TweenSize and the TweenPosition methods to work, but for some reason the methods are no longer working. They worked a few days ago, then suddenly they stopped working for some reason. I know it's not a script error because I get no errors when I access the developer console, and only the GUI's that have a TweenSize or TweenPosition method in them are not working. I'll provide some code:

function LevelUp(Player,Rank)
    local LevelUp = script.LevelUp:Clone()
    local Main = LevelUp.Frame
    Main.RankImage.Image = _G.Ranks[Rank][4]
    LevelUp.Parent = Player.PlayerGui
    Main.RankImage:TweenSizeAndPosition( --This is the line that doesn't work. It doesn't error or anything like that, it just doesn't work. All the code underneath it works though
        UDim2.new(0,60,0,80),
        UDim2.new(0.5,-30,0,0),
        Enum.EasingDirection.Out,
        Enum.EasingStyle.Linear,
        0.2
    )
    wait(0.2)
    Main.RankNum.Text = "Rank: "..Rank
    local TitleText = "You have ranked up!"
    for i = 1,string.len(TitleText) do
        Main.Title.Text = string.sub(TitleText,1,i)
        wait(1/20)
    end
    wait(4)
    LevelUp:Destroy()
end

Here's another block of code:

local NextRankXP = _G.Ranks[NextRank2][2]
local RankScale = (PlayerXP - _G.Ranks[PlayerRank][2]) / (NextRankXP - _G.Ranks[PlayerRank][2])
RankBar.Tray:TweenSize(UDim2.new(RankScale,0,1,0),"Out","Sine",0.5) --Again, this doesn't work

Note #1: These lines of code are in normal scripts, not in LocalScripts, but that shouldn't be the problem because they were working before in normal scripts

Note #2: The tween methods work just find in play solo mode and in server mode, but not in play mode

Please help!