If I put the ad units into my template individually as shown in my initial post, both ad units load on both desktop and on mobile.
If I put the ad group into my template (which does have “Enable mobile support” checked) then I get NO ads at all on desktop, but I do get the mobile only ad on mobile. Here is the message I get on desktop when I use this method:
<!– Either there are no banners, they are disabled or none qualified for this location! –>