Why does this stop?

When you call WaitForChild, you're checking for the sticker value instead of the sticker. Just change it to check for the sticker you're searching for.

The code you posted might not be sufficient to find a solution. I don't know what you're storing in the table, or how they might be indexed, so that might also be a problem. Let me know if this code doesn't work.

function update()
    print("upd8")
    JumpValu = 50
    for i=1,8 do
    local sticker = stickers["Sticker"..i]
    local StickerValue = sticker.Value
    if StickerValue~="" and StickerValue~="LOCKED" then
        if game.ServerStorage.assets.stickers:WaitForChild(sticker):FindFirstChild("Jump") then
            JumpValu = JumpValu + game.ServerStorage.assets.stickers:WaitForChild(sticker):FindFirstChild("Jump").Value
        end
    end
    end
    print("lol")
end

update()

You did not call the function. Do this:

JumpValu = 50

function update()
    print("upd8")
    JumpValu = 50
    for i=1,8 do
    local StickerValue = stickers["Sticker"..i].Value
    if StickerValue~="" and StickerValue~="LOCKED" then
        if game.ServerStorage.assets.stickers:WaitForChild(StickerValue):FindFirstChild("Jump") then
            JumpValu = JumpValu + game.ServerStorage.assets.stickers:WaitForChild(StickerValue):FindFirstChild("Jump").Value
        end
    end
    end
    print("lol")
end

update()