We saw this with a few of the EER moderators -- they didn't receive the activation message on stg, so they couldn't activate their account:
https://journalpub-stg.escholarship.org/admin/core/account/15277/change/?_changelist_filters=q%3Dmcpheeters

I remember we didn't receive a bounce notice, so we don't know why it was happening. But the user can simply reset their password to activate their account, or we can tick the "Is Active" box in the Janeway admin view.