Script stopping, no errors?

I wrote a code down below that's supposed to counteract gravity in parts that the "manipulator" part is pointing at. However, sometimes the loop in the function "manipulate" runs once, twice, or not at all. I know that it's not the if statement on line 10 that's stopping the code, because I tried to troubleshoot my code there by printing a phrase, and it didn't print anything. Any help?

local event = Instance.new("RemoteEvent",game.ReplicatedFirst)
event.Name = "descendantadded"

local parts = {}

local function manipulate(manipulator,part)
    coroutine.resume(coroutine.create(function()
        local n
        while true do
            if not manipulator or not part then
                return
            end
            local p = manipulator:pointToObjectSpace(part.Position)
            if p.x <= -manipulator.Size.x/2 and
            p.x >= -manipulator.Size.x/2 and
            p.z <= -manipulator.Size.z/2 and
            p.z >= -manipulator.Size.z/2 and
            p.y >= manipulator.Size.y/2 then
                if not part:FindFirstChild("NoGravity") then
                    n = Instance.new("BodyForce",part)
                    n.Name = "NoGravity"
                end
                n.Force = Vector3.new(0,196.2,0)*part:GetMass()
            else
                if part:FindFirstChild("NoGravity") then
                    n:Destroy()
                end
            end
            game:GetService("RunService").RenderStepped:wait()
        end
    end))
end


local function findparts(manipulator)
    event.OnServerEvent:connect(function(nothing,descendant)
        manipulate(manipulator,descendant)
    end)
    for i,v in pairs(parts) do
        manipulate(manipulator,v)
    end
end

workspace.DescendantAdded:connect(function(descendant)
    if descendant:IsA("Part") and descendant.Name ~= "Baseplate" then
        if descendant.Name == "Gravity Manipulator" then
            findparts(descendant)
        else
            table.insert(parts,#parts+1,descendant)
            event:FireServer(descendant)
        end
    end
end)

workspace.DescendantRemoving:connect(function(descendant)
    for i,v in pairs(parts) do
        if v == descendant then
            table.remove(parts,i)
            break
        end
    end
end)

local function indexparts(instance)
    local children = instance:GetChildren()
    if #children > 0 then
        for i,v in pairs(children) do
            if #v:GetChildren() > 0 then
                indexparts(v)
            end
            if v:IsA("Part") and v.Name ~= "Baseplate" then
                if v.Name == "Gravity Manipulator" then
                    findparts(v)
                else
                    table.insert(parts,#parts+1,v)
                end
            end
        end
    end
end

indexparts(workspace)