Some users are suddenly experiencing an error while entering the standard date field in a lightning page. No change has been made to the field. Her time zone is correct, and no change has been made to the company time zone. Error - 'your entry does not match the allowed format MMM d yyyy'.. If they are choosing a date from the calendar icon in the date field it initially shows up as Dec 12, 2019 and then they can edit the 2019 to 2199.