Picker field Issue: All users must be valid and visible to the viewer

Hi all,

   I am facing an issue in the picker field, I want to select multiple users from all user groups(cons!STM_GROUP_ALL_USER). When I select the 2nd user name it through this error message  All users must be valid and visible to the viewer. Can anyone help me to figure out this?

a!pickerFieldUsers(
                label: "Watchers",
                labelPosition: "ABOVE",
                maxselections: 5,
                groupFilter:cons!STM_GROUP_ALL_USER,
                value:{index(ri!watchers,"userName",{})},
                saveInto: {
                  ri!watchers.userName,
                  a!save(
                    ri!watchers.role,
                    "Watcher"
                  )
                },
                validations: {}
              ),

 Discussion posts and replies are publicly visible