Can't seem to get mongo_tail to work

[rosslutsch]

seems to connect to mongo but then nothing, no errrors etc, I've added more entries to the collection and still nothing, shouldn't the colelction be logged to stdout here?

<ROOT>
  <source>
    @type mongo_tail
    tag "app.mongo_log"
    wait_time 5
    time_key "time"
    collection "transcripts"
    url "mongodb://root:*****@localhost:27017/dev/?authSource=admin&replicaSet=rs0&readPreference=secondaryPreferred"
  </source>
  <source>
    @type http
    port 9880
  </source>
  <match **>
    @type stdout
  </match>
</ROOT>
2021-04-01 12:48:58 +0000 [info]: starting fluentd-1.12.0 pid=7 ruby="2.5.8"
2021-04-01 12:48:58 +0000 [info]: spawn command to main:  cmdline=["/usr/bin/ruby", "-Eascii-8bit:ascii-8bit", "/usr/bin/fluentd", "-c", "/fluentd/etc/fluentd.conf", "-p", "/fluentd/plugins", "--under-supervisor"]
2021-04-01 12:49:00 +0000 [info]: adding match pattern="**" type="stdout"
2021-04-01 12:49:00 +0000 [info]: adding source type="mongo_tail"
2021-04-01 12:49:02 +0000 [info]: adding source type="http"
2021-04-01 12:49:02 +0000 [warn]: #0 define <match fluent.**> to capture fluentd logs in top level is deprecated. Use <label @FLUENT_LOG> instead
2021-04-01 12:49:02 +0000 [info]: #0 starting fluentd worker pid=20 ppid=7 worker=0
2021-04-01 12:49:02.095505443 +0000 fluent.info: {"pid":20,"ppid":7,"worker":0,"message":"starting fluentd worker pid=20 ppid=7 worker=0"}
2021-04-01 12:49:02 +0000 [info]: #0 fluentd worker is now running worker=0
2021-04-01 12:49:02.479606766 +0000 fluent.info: {"worker":0,"message":"fluentd worker is now running worker=0"}