Went to update my MacOS app on the Connect site. After I clicked on + on the Distribution page, I thought it was weird that my artwork was missing, so I tried to re-add my prior artwork. This was blocked with the message "Please save new locales before uploading screenshots". I only have en-us as a locale, that hasn't changed. So now I can't update it.
Cannot update MacOS app, "Please save new locales"
And today the screenshot magically showed up in the Draft submission. Phew! Submitted.