Am having intermittent trouble entering death dates. Sometimes I can, sometimes I can't, sometimes it takes the year but not the full date. It was working for a while, now it's not (again).
Do not enter "comma"; that is the issue. Once the fix is finished, we will be able to enter and to cut and paste in date strings with "comma" in them again.
Look to the right of the date field at the gray italics and see if the year "took" or not.