How to fix issues caused by latency between local and server scripts?

I've been having trouble getting my FilteringEnabled scripts to work lately. This mostly includes bugs such as too many objects being created or values being made out of sync. These errors mostly result from the client spamming UserInput.

I've tried adding debounces, buffers, delays, etc., but no matter how many methods I use, the client is still able to cause something abnormal to happen, that shouldn't.

It doesn't necessarily break the game, since most people won't be spamming their keyboard, but with enough dedication, it's not difficult to break certain aspects of the game.

My LocalScript relies a lot on the server sending back the correct value, and even waits before returning these values (as a bit of a buffer) but still, my part variable is sometimes incorrectly nil. Here's my UserInput code, which I find to be most responsible. My main issue is often when spam sending the server part at line 15, it's nil, when it should be a part in a Workspace Folder, as defined in line 7.

UserInput.InputBegan:Connect(function(input, ignore)
    if input.UserInputType == Enum.UserInputType.Keyboard then
        if input.KeyCode == Key and using == false then
            for i = 1, #parts do
                local magnitude = (char.Humanoid.RootPart.Position - parts[i].Position).Magnitude
                if magnitude <= range then
                    buffer, part = use:InvokeServer(parts[i], char) --part returns the part used
                    if buffer == true then
                        wait(.5)
                        using = true
                    end
                end
            end
        elseif input.KeyCode == Key or input.KeyCode == Enum.KeyCode.Space and using == true then
            buffer, part = stopuse:InvokeServer(part, char) --returns part as nil.
            if buffer == false then
                wait(.5)
                using = false
            end
        end
    end
end)

I believe that my best solution is to add waits to parts of the UserInput, but I do not know the appropriate places to put these waits.