Shortening Currencies Value Doesn't Work For Second Currency?

Your using 2 while loops, so the game reads it from top to bottom, and it will loop over the first While Loop until it breaks. If it doesn't break, it'll just loop over that current code for the rest of the game being live.

To fix this, I used a ModuleScript with functions and just looped those. I may have done it a bit more complicated and memory consuming than it had to be, but I just found this way to be easier for me.

In the ModuleScript that I named NumericalShortener I changed it around.

local numericalShortener = {}

function numericalShortener.ShortenChi(player)
    local chi = tostring(player:WaitForChild("MainCurrency"):FindFirstChild("Chi").Value)
    local chiDis = player:WaitForChild("leaderstats"):FindFirstChild("Chi")

    if #chi >= 10 then
        chiDis.Value = chi:sub(0,(#chi - 9)).."."..(chi:sub(#chi - 7,(#chi - 7))).."B+"
    elseif #chi >= 7 then
        chiDis.Value = chi:sub(0,(#chi - 6)).."."..(chi:sub(#chi - 5,(#chi - 5))).."M+"
    elseif #chi >= 4 then
        chiDis.Value = chi:sub(0,(#chi - 3)).."."..(chi:sub(#chi - 2,(#chi - 2))).."K+"
    else
        chiDis.Value = chi
    end
end

function numericalShortener.ShoternCoins(player)
    local coins = tostring(player:WaitForChild("MainCurrency"):FindFirstChild("Coins").Value)
    local coinsDis = player:WaitForChild("leaderstats"):FindFirstChild("Coins")

    if #coins >= 10 then
        coinsDis.Value = coins:sub(0,(#coins - 9)).."."..(coins:sub(#coins - 7,(#coins - 7))).."B+"
    elseif #coins >= 7 then
        coinsDis.Value = coins:sub(0,(#coins - 6)).."."..(coins:sub(#coins - 5,(#coins - 5))).."M+"
    elseif #coins >= 4 then
        coinsDis.Value = coins:sub(0,(#coins - 3)).."."..(coins:sub(#coins - 2,(#coins - 2))).."K+"
    else
        coinsDis.Value = coins
    end
end

return numericalShortener

In a ServerScript that I named CurrencyHandler I added a loop for the functions of the ModuleScript while requiring it.

local moduleShortener = require(script.NumericalShortener)

game.Players.PlayerAdded:Connect(function(plr)
    local leaderstats = Instance.new("Folder", plr)
    leaderstats.Name = "leaderstats"

    local MainCurrency = Instance.new("Folder", plr)
    MainCurrency.Name = "MainCurrency"

    local Coins = Instance.new("IntValue", MainCurrency)
    Coins.Name = "Coins"
    Coins.Value = 0

    local Chi = Instance.new("IntValue", MainCurrency)
    Chi.Name = "Chi"
    Chi.Value = 0

    local CoinsDis = Instance.new("StringValue", leaderstats)
    CoinsDis.Name = "Coins"
    CoinsDis.Value = 0

    local Gems = Instance.new("IntValue", leaderstats)
    Gems.Name = "Gems"
    Gems.Value = 0

    local ChiDisp = Instance.new("StringValue", leaderstats)
    ChiDisp.Name = "Chi"
    ChiDisp.Value = 0

    local Strength = Instance.new("IntValue", leaderstats)
    Strength.Name = "Strength"
    Strength.Value = 0

    local MaxStrength = Instance.new("IntValue", leaderstats)
    MaxStrength.Name = "MaxStrength"
    MaxStrength.Value = 10

    while wait() do
        moduleShortener.ShortenChi(plr)
        moduleShortener.ShoternCoins(plr)
    end
end)

This is how I have it set up in ServerScriptService, here.

Hope this helped! I'm pretty sure this should work as I have tested it myself.

If this is what you're looking for and it helped, let me know by selecting this as the answer!

Tried This But The Chi's Value Won't Change Now?

game.Players.PlayerAdded:Connect(function(plr)
    local leaderstats = Instance.new("Folder", plr)
    leaderstats.Name = "leaderstats"

    local MainCurrency = Instance.new("Folder", plr)
    MainCurrency.Name = "MainCurrency"

    local Coins = Instance.new("IntValue", MainCurrency)
    Coins.Name = "Coins"
    Coins.Value = 0

    local Chi = Instance.new("IntValue", MainCurrency)
    Chi.Name = "Chi"
    Chi.Value = 0

    local CoinsDis = Instance.new("StringValue", leaderstats)
    CoinsDis.Name = "Coins"
    CoinsDis.Value = 10

    local Gems = Instance.new("IntValue", leaderstats)
    Gems.Name = "Gems"
    Gems.Value = 0

    local ChiDisp = Instance.new("StringValue", leaderstats)
    ChiDisp.Name = "Chi"
    ChiDisp.Value = 10

    local Strength = Instance.new("IntValue", leaderstats)
    Strength.Name = "Strength"
    Strength.Value = 0

    local MaxStrength = Instance.new("IntValue", leaderstats)
    MaxStrength.Name = "MaxStrength"
    MaxStrength.Value = 10

    while wait() do --COIN COVERT
        local Coin = tostring(Coins.Value)
        if #Coin >= 10 then -- Bill
            CoinsDis.Value = Coin:sub(0,(#Coin-9)).."."..(Coin:sub(#Coin-7,(#Coin-7))).."B+"
        elseif #Coin >= 7 then -- Mill
            CoinsDis.Value = Coin:sub(0,(#Coin-6)).."."..(Coin:sub(#Coin-5,(#Coin-5))).."M+"
        elseif #Coin >= 4 then -- Thos
            CoinsDis.Value = Coin:sub(0,(#Coin-3)).."."..(Coin:sub(#Coin-2,(#Coin-2))).."K+"
        else
            CoinsDis.Value = tostring(Coins.Value)
        end 

        local Chi = tostring(Chi.Value)
        if #Chi >= 10 then -- Bill
            ChiDisp.Value = Chi:sub(0,(#Chi-9)).."."..(Chi:sub(#Chi-7,(#Chi-7))).."B+"
        elseif #Chi >= 7 then -- Mill
            ChiDisp.Value = Chi:sub(0,(#Chi-6)).."."..(Chi:sub(#Chi-5,(#Chi-5))).."M+"
        elseif #Chi >= 4 then -- Thos
            ChiDisp.Value = Chi:sub(0,(#Chi-3)).."."..(Chi:sub(#Chi-2,(#Chi-2))).."K+"
        else
            ChiDisp.Value = tostring(Chi.Value)
        end         
    end

end)