1.1: A user reports that his Task Manager shows the graphics card idle while rendering in Lumion
Hello
Thanks for the question.
Everything is working fine for you. What is happening, due to the under-the-hood changes of Lumion, is that Windows Task Manager does not display the usage of the graphics card correctly. This is not an issue that strictly affects Lumion, but also other applications using a similar engine.
As you are probably aware, Lumion works based on a game engine and, lately, the gaming community has been fairly vocal about how terribly Microsoft is managing their Task Manager in regards to displaying the graphics card usage. Previous versions (up to Lumion 10.5) were being displayed correctly.
For situations like this, our developers recommend using either MSI Afterburner (with the Hardware Monitor turned on) or GPU-Z (Sensors tab) to monitor the usage of the GPU. This will show the true capacity at which the graphics card is being used. 
Does that make sense?
3.1: Reference: Zendesk Support Request
3.2: Applicable to: