Unable to drag files from desktop across desktops now that an external screen has been added
I frequently will drag files saved on my desktop across desktops to a full screen window (i.e. to attach images to email). This has always worked beautifully. Now that I've changed my setup with my MacBook Pro to include an additional 32" screen (woohoo!), I can no longer use this function in the same way. I can drag items to the external screen, but I cannot drag them between desktops on the MacBook. As soon as the external screen is disconnected, the functionality returns.
Any way around this?
MacBook Pro 13”, macOS 10.14