I had tried a few different things to fix the issue including changing the number of desktop screens, changing the background, changing the way icons appear on the desktop and restarting the machine. I found a bug report of the issue, which apparently has persisted in more recent releases of macOS, including Catalina. The ‘fix’ isn’t quite a fix, as the issue can return at random, but its simple enough that the issue isn’t too painful. Simply close and restart the Finder app, by pressing Alt and right-clicking the Finder icon, then selecting Relaunch from the pop-up menu.