Why does the_date work in the first custom column, but not in the second, in a series of customized Posts columns?

1) the_date() echoes the date value, so this statement isn’t correct:

echo the_date('d M');

It should be:

the_date('d M');

2) If you have some posts posted on the same date, the_date() will show only the date value for the 1st post. There will be no result for remained posts.

To get date of all post, use get_the_date() (which returns date value) or the_time() instead.