Why is my Region3 being inconsistent?

I am working on a building system for my game, and I check if you are building on your plot by creating a temporary part where you are attempting to build, and if it is in the Region3 of that plot, then it places the object. My problem is that after some blocks have been placed, some regions of the Region3 go unchecked, returning that the temporary part is not in the region.

Video Example

Code:

game.ReplicatedStorage.Buildables.reqBuild.OnServerEvent:Connect(function(player, pos, item, color, material, color2, material2, hazard)

    local function build()
        local piece = game.ReplicatedStorage.Buildables:WaitForChild(item)
        local part = piece:Clone()
        part:SetPrimaryPartCFrame(pos)
        for _, object in pairs(part:GetChildren()) do
            -- Decorates object
        end
        part.Parent = game.Workspace.Placed_Blocks
        game.ReplicatedStorage.Buildables.reqBuild:FireClient(player)
    end

    local tempPart = Instance.new("Part")
    tempPart.Size = Vector3.new(1, 1, 1)
    tempPart.CanCollide = false
    tempPart.Transparency = 1
    tempPart.Position = pos.p -- Requested position from CFrame to Vector3
    tempPart.Parent = workspace.Ignore_Blocks
    tempPart.Name = "tempPart_" .. player.Name
    tempPart.Anchored = true
    workspace.Ignore_Blocks:WaitForChild("tempPart_" .. player.Name)
    for _, object in pairs(workspace.Stuff.Build_Plates:GetChildren()) do
        if object.Owner.Value == player.Name then
            --The buildplate has 2 Vector3 values for the corners of the area.
            --Corner1 contains the lowest values, Corner2 contains the higher
            local region = Region3.new(object.Corner1.Value, object.Corner2.Value)
            for _, object in pairs(workspace:FindPartsInRegion3(region)) do
                print(object.Name)
                if object == tempPart then
                    tempPart:Destroy()
                    tempPart = nil
                    build()
                end
            end
            region = nil
            if tempPart then
                tempPart:Destroy()
                tempPart = nil
                game.ReplicatedStorage.Buildables.reqBuild:FireClient(player)
            end
        end
    end

end)