I wonder if this is a (VERY minor) consequence of changing time...
I'm scheduled to fly tomorrow at 11:30a. I got an email time stamped at 10:29a today saying "It's time to check in!" (normally 24 hours before flight). I wasn't paying attention to the time, went to my Delta app and go the message "It's too early to check in."
10:29a today will be 11:29a tomorrow. Maybe Delta changed the clocks on their email notification system a day early?