Dynamic Data Attachments - problems when retrieving data form select-multiple options

Using dynamic data attachments, I was trying to retrive data from an pre-existing form. The situation would be:

Parental KOBO:

type | name | label
begin_group | identification | Patient identification
text | nm | name:
end_group | identification | Patient identification
| |
begin_group | case_data | Patient data
text | sym_onset | Symptoms onset date:
select_multiple sym | sym_all | Select the symptoms you had:
end_group | case_data | Patient data

Child KOBO:

type | name | label | calculation
xml-external | survey | |
begin_group | C_identification | Patient identification |
text | C_nm | Name: |
text | C_birth | Birth date: | OBS1
end_group | C_identification | Patient identification |
| | |
begin_group | C_symptoms | Patient data |
text | sym_onset | Symptoms onset: | OBS2
select_multiple sym | sym_all | Symptoms you had: | OBS3
end_group | C_symptoms | Patient data |

OBS1 = Working
instance(‘survey’)/root/data[identification/nm = current()/…/C_nm]/identification/birth

OBS2 = Not working
instance(‘survey’)/root/data[identification/nm = current()/…/C_nm]/case_data/sym_onset

OBS3 = Not working
instance(‘survey’)/root/data[identification/nm = current()/…/C_nm]/case_data/sym_all

Does anyone have some insight on why it’s not working?
Thanks in advance

@victorota, have you gone through our support article Dynamic Data Attachment? It should solve your issue: