A custom field is missing on a card

In my wekan board, the Sex field does not show on some cards but it shows on others. Why is that ?

The Sex field is a Custom field in wekan, meaning it was defined by the user like so:

a

When it is defined after cards were created, it will not show automatically. You have to go the hamburger menu of the card (top right corner):

b

And add it explicitly using the Edit custom field menu entry:

c

I will then show on the card and you will be able to edit it:

d

Note however that you will not need to do this for cards that were created after the custom field.

e