Hi m.caplan,
Thanks for using Apple Support Communities. It sounds like you're on the right path for setting up aerial wallpaper shuffling. We'd recommend checking to make sure you have the right selection for how often they shuffle as well. The following is from Customize the wallpaper on your Mac - Apple Support.
On your Mac, choose Apple menu
> System Settings, then click Wallpaper
in the sidebar. (You may need to scroll down.)
Select a wallpaper from one of the available categories:
• Add Photo/Add Folder or Album: Controls to choose your own images.
• Dynamic Wallpapers: These images brighten and darken, based on the time of day for your current location.
• Landscape, Cityscape, Underwater, and Earth aerials: These still images show dramatic views.
• Shuffle Aerials: These still images change at an interval you set.
• Pictures: These still images show creative pictures.
• Colors: These swatches apply a solid-color background for your desktop.
Set options for your wallpaper.
Options vary based on the wallpaper you choose. For example, you can:
• Turn on a slow-motion aerial as a screen saver, using the still aerial of your wallpaper.
• Choose how often to shuffle through aerials.
• Choose light or dark still versions of Dynamic Wallpaper.
• Add your own color.
If everything looks good there, it may be best to have Apple Support look in to it further. You can reach out from Get Support.
All the best.