Field Not Showing in Member Directory (Intermittent)

I have an Ultimate Member registration form, actually 2 registration forms, one french and one english. I have a field that exists in both forms, and if I look at the registration details on a user in the backend, the fields are all complete. However, if I look at that same user in the member directory on the front end, one of the fields is missing. For some reason though, for other users the field is present. What might be causing this?

Thanks.

Glen