попробуйте использовать:
xml_find_all(doc, ".//*[name()='sanctionEntity']")
{xml_nodeset (2)}
[1] <sanctionEntity designationDetails="" unitedNationId="" euReferenceNumber="EU.36.64" logicalId="1">\n ...
[2] <sanctionEntity designationDate="2002-02-21" designationDetails="" unitedNationId="" euReferenceNumber= ..
xml_find_all(doc, ".//*[name()='sanctionEntity']") %>% map(xml_find_all, "./*")
[[1]]
{xml_nodeset (5)}
[1] <regulation regulationType="amendment" organisationType="commission" publicationDate="2018-02-16" entry ...
[2] <subjectType code="person" classificationCode="P"/>
[3] <nameAlias firstName="Robert" middleName="Gabriel" lastName="Mugabe" wholeName="Robert Gabriel Mugabe" ...
[4] <birthdate circa="false" calendarType="GREGORIAN" city="" zipCode="" birthdate="1924-02-21" dayOfMonth= ...
[5] <identification diplomatic="false" knownExpired="false" knownFalse="false" reportedLost="false" revoked ...
[[2]]
{xml_nodeset (5)}
[1] <remark>Date of designation referred to in Article 7 (2): 21.2.2002.</remark>
[2] <regulation regulationType="amendment" organisationType="commission" publicationDate="2002-09-13" entry ...
[3] <subjectType code="person" classificationCode="P"/>
[4] <nameAlias firstName="Robert" middleName="Gabriel" lastName="Mugabe" wholeName="Robert Gabriel Mugabe" ...
[5] <birthdate circa="false" calendarType="GREGORIAN" city="Kutama" zipCode="" birthdate="1924-02-21" dayOf ...