Restarting HDMI output

I am having trouble restarting the output pipeline on my ZCU104 board.

First, I am configuring and starting the output piple, generate a test image and can successfully verify that the test image appears on my screen.
Then I stop the HDMi output to simulate an unconnected cable.
When I now again start the HDMI output, in the same manner as before, I do not get any error message or timeout, but also there is no image appearing on my monitor screen.
Is it expected that using the sequence of hdmi_out.start(), hdmi_out.stop(), hdmi_out.start() does not restart the pipeline?

Here is the code for the function. I execute this function twice. When executing first, after loading the overlay, I get the test image on the screen. When executing it the second time, there is no image on the screen.

def sent_test_image_to_screen():
    hdmi_out =
    mode = VideoMode(1920, 1080, 24)

    ref_frame = np.ndarray(shape=.mode.shape, dtype=np.uint8)

    out_frame = hdmi_out.newframe()
    out_frame[:] = ref_frame