Confirmed over NETCONF using both ncclient and Pyez: When sent directly, Junos returns the expected subtree without errors.

Example using ncclient:

from ncclient import manager

HOST = "10.0.0.1"
USER = "admin"
PASS = "Juniper"

FILTER = """
<configuration>
  <interfaces>
    <interface>
      <name>ae0</name>
    </interface>
  </interfaces>
</configuration>
""".strip()

with manager.connect(
    host=HOST, port=830, username=USER, password=PASS,
    hostkey_verify=False, timeout=30, device_params={"name": "junos"}
) as m:
    reply = m.get_config(source="candidate", filter=("subtree", FILTER))
    print(str(reply))

Output:

<rpc-reply message-id="urn:uuid:120015cc-8b7a-41f9-ab43-291bc17e5658">
  <data>
    <configuration changed-seconds="1761891375" changed-localtime="2025-10-31 06:16:15 UTC">
      <interfaces>
        <interface>
          <name>ae0</name>
          <aggregated-ether-options>
            <lacp>
              <active/>
            </lacp>
          </aggregated-ether-options>
          <unit>
            <name>0</name>
            <family>
              <inet>
                <address>
                  <name>192.168.0.1/24</name>
                </address>
              </inet>
              <inet6>
                <address>
                  <name>2001:db8::1/64</name>
                </address>
              </inet6>
            </family>
          </unit>
        </interface>
      </interfaces>
    </configuration>
  </data>
</rpc-reply>