Script has suddenly broken after barely changing it (building tools script)? [SOLVED]

I was just making a game called "Mayor Sphereoid's Community Place" and I was trying to create build tools. To add some context to why I'm not using the Tool instance, the characters are not humanoids but they are balls with custom controls and a custom camera, meaning that most things compatible with a normal Roblox avatar won't work with my characters.

In my game, there is: A remote function, PartFunction, used to run part functions as a client A remote event, PartMod, used to change values of parts as a client A custom configuration folder put inside a player instance containing the currently held tool

These scripts worked a minute ago and I barely changed anything!

ServerScriptService PartMod (Script)

game.ReplicatedStorage:WaitForChild("PartMod").OnServerEvent:Connect(function(player, part, attr, value, operation)
    if operation == "add" then
        part[attr] = part[attr] + value
    elseif operation == "multiply" then
        part[attr] = part[attr] * value
    else
        part[attr] = value
    end
end)

game.ReplicatedStorage:WaitForChild("PartFunction").OnServerInvoke = function(player, part, func, ...)
    if func == "Clone" then
        local result = part:Clone()
        result.Parent = game.ReplicatedStorage.StoredParts
        result.Name = string.format("%x", math.random(0, 15)) .. "x" .. string.format("%x", player.UserId)
        return {name=part.Name, key=result.Name}
    elseif func == "Destroy" then
        part:Destroy()
    elseif func == "Resize" then
        local testPart = part:Clone()
        testPart:Resize(...)
        if testPart.Size.X <= 0.05
            or testPart.Size.Y <= 0.05
            or testPart.Size.Z <= 0.05 then
            testPart:Destroy()
            return false
        end
        testPart:Destroy()
        return part:Resize(...)
    end
end

StarterPlayerScripts ToolControl (LocalScript)

local player = game.Players.LocalPlayer
local config = player:WaitForChild("Configuration")
local mouse = player:GetMouse()
local rs = game.ReplicatedStorage

local partMod = function(...) rs.PartMod:FireServer(...) end
local partFunc = function(...) return rs.PartFunction:InvokeServer(...) end

-- partMod(part, attr, val, [operation])
-- partFunc(part, func, ...)

local part = nil
local handles = Instance.new("Handles", player.PlayerGui)
local ogMoveDistance = 0
local ogResizeDistance = 0

local function round(x, y)
    return math.floor(x / y + 0.5) * y
end

local function handleHandlerInit()
    ogMoveDistance = 0
    ogResizeDistance = 0
end

local function handleHandler(face, distance)
    local inc = 0.25
    if face == Enum.NormalId.Top or face == Enum.NormalId.Bottom then
        inc = inc * 1.2
    end

    -- Resize

    if config.Tool.Value == "resize" then
        distance = distance / 4
        local delta = distance - ogResizeDistance
        if math.abs(delta) >= inc then
            local sizeDelta = math.floor(delta / inc + 0.5) * inc
            print(sizeDelta)
            if partFunc(part, "Resize", face, sizeDelta) then
                ogResizeDistance = distance
            end
        end

    -- Move

    elseif config.Tool.Value == "move" then
        local delta = distance - ogMoveDistance
        if math.abs(delta) >= inc then
            local sizeDelta = math.floor(delta / inc + 0.5) * inc
            partMod(part, "CFrame", CFrame.new(Vector3.FromNormalId(face) * sizeDelta), "multiply")
            ogMoveDistance = distance
        end
    end
end

handles.Name = "BToolHandles"
handles.MouseButton1Down:Connect(handleHandlerInit)
handles.MouseDrag:Connect(handleHandler)

game:GetService("UserInputService").InputBegan:Connect(function(key)
    if key.UserInputType == Enum.UserInputType.MouseButton1
        and key.UserInputState == Enum.UserInputState.Begin then
        if mouse.Target 
            and mouse.X < mouse.ViewSizeX - 90 then

            if mouse.Target.Parent == workspace.BuildingParts then

                -- Clone tool

                if config.Tool.Value == "clone" then
                    local info = partFunc(mouse.Target, "Clone")
                    part = rs.StoredParts:FindFirstChild(info.key)
                    partMod(part, "CFrame", CFrame.new(0, part.Size.Y, 0), "multiply")
                    partMod(part, "Name", info.name)

                    if not part:FindFirstChild("Ownership") then
                        local ownership = Instance.new("IntValue", part)
                        ownership.Name = "Ownership"
                        ownership.Value = player.UserId
                    end

                    partMod(part, "Parent", workspace.BuildingParts)
                end

                -- Select tool

                if config.Tool.Value == "select"
                    and not mouse.Target.Locked
                    and part.Ownership then
                    if part.Ownership.Value == player.UserId then
                        handles.Adornee = part
                    end

                -- Destroy tool

                if config.Tool.Value == "destroy"
                    and not mouse.Target.Locked
                    and part:FindFirstChild("Ownership") then
                    if part.Ownership.Value == player.UserId then
                        partFunc(mouse.Target, "Destroy")
                    end
                end
            end

        -- Remove unused handles
        elseif config.Tool.Value == "select"
            and mouse.X < mouse.ViewSizeX - 90 then
            handles.Adornee = nil
        end
    end
end)

This is just so weird! Please help immediately!

NOTES:

I wanted to make it so that parts can't go to 0.05x0.05x0.05 size

I have a control panel on the right which I don't want anyone to click through (hence mouse.X < mouse.ViewSizeX - 90)

There are no errors that appear!

Edit: There is an error that appears, actually. Look at my answer for more info.