This is happening to me as well. Ryzen 2200G an a Gigabyte AB350N. First monitor is a TV, LG UH15A, and my second monitor is a tablet remote displayed over spacedesk. Trying to put the marquee on the 2nd screen puts it behind the main display.
On my Asus laptop it worked just fine as marquee monitor, regardless of it i was using the laptop screen or my TV via HDMI.
It's not the end of the world. The tablets main Purpose is to display the WiiU Gamepad visuals, it was just nice to have it do marquee stuff for systems other than WiiU.