User Picker field (group-filtered) not showing selectable users for some end users

[joanna_natial]

On the request form in Jira, a User Picker field is currently configured with a group-based filter. However, some end users are unable to see or select any users in this field.

Is the field configuration (group filter) restricting visibility beyond expected behaviour?

Does the end user need access to the project, group, or directory to see available users?