Can't access grandparent node through ancestor axis

Ancestor axis can't access the grand parent nodes of the data. The following apis are not returning any data.

curl -g --user cpsuser:cpsr0cks! --request GET 'http://localhost:8883/cps/api/v1/dataspaces/E2EDemo/anchors/ran-network-anchor/nodes/query?cps-path=//sNSSAIList[@sNssai="111-1111"]/ancestor::NRCellDU'

Response: {}

curl -g --user cpsuser:cpsr0cks! --request GET 'http://localhost:8883/cps/api/v1/dataspaces/E2EDemo/anchors/ran-network-anchor/nodes/query?cps-path=//sNSSAIList[@sNssai="111-1111"]/ancestor::GNBDUFunction&include-descendants=true'

Response: {}