error parsing identity

In polling a model using RESTCONF I hit errors parsing the response from the NETCONF plug-in.

The URL I'm polling is:

/restconf/operational/opendaylight-inventory:nodes/node/ncs/yang-ext:mount/tailf-ncs:devices/device/CSR1KV-1/

The NETCONF response from NCS is correct, but I get an HTTP500 error from RESTconf with:
"error-type": "application",
"error-tag": "operation-failed",
"error-message": "read execution failed",

however no error is logged in opendaylight.log.

If I go to a more specific API call, e.g.:

/restconf/operational/opendaylight-inventory:nodes/node/ncs/yang-ext:mount/tailf-ncs:devices/device/CSR1KV-1/config

then ODL parses the response and displays it as XML.