REST API: Problem with getting build artifact information

I'm using the shell script below inside a TC build configuration to (try to) retrieve the artifacts information of another build using the REST API.

  build=$(curl -q -X GET -H "Authorization: Bearer $TOKEN" -H "Accept: application/json" \
      https://TEAMCITY/app/rest/builds/id:$id/artifacts/children | tr '\n' ' ')
  count="$(echo $build | jq -r '.count')"
  iter=0
  while [ $count -eq 0 ] && [ $iter -lt 10 ];
  do
    sleep 60
    iter=$((iter + 1))
    build=$(curl -q -X GET -H "Authorization: Bearer $TOKEN" -H "Accept: application/json" \
        https://TEAMCITY/app/rest/builds/id:$id/artifacts/children)
    count="$(echo $build | jq -r '.count')"
  done

I've checked - also via the REST API - that the build has completed before the above code runs. I've tried waiting even 30minutes after the build finishes, but no joy. I keep getting

{"count":0,"file":[]}

I am getting the artifacts of a different build within the same shell script and that always works.

A long time later, I just tried it from the command-line for the same build ID which failed, and I get the correct response.