Tsung testing not opening sessions for users in ejabberd

Hi - I'm trying to load test my ejabberd XMPP server with random messages that the Tsung client should send. Whilst I was earlier able to successfully register multiple users on the chat server, I'm somehow not able to get any of these users get online and / or send chat messages to others. Below is my Tsung xml. Might you be able to advise please what could be going wrong here - something I'm overlooking in my xml or a server setting?

The ejabberd logs do show "Accepted authentication for ..." for users, but they dont go beyond. If I login manually via a web client to the server, the server logs show "Opened session for...", so clearly there is a step that is getting missed here...

Thanks much...

Tsung xml:

<?xml version="1.0"?>
<!DOCTYPE tsung SYSTEM "/usr/local/share/tsung/tsung-1.0.dtd">
<tsung loglevel="notice" version="1.0">

  <clients>
    <client host="localhost" use_controller_vm="true"></client>
  </clients>

  <!-- Server side setup -->
 <servers>
  <server host="ip-xx-xx-xx-xx" port="5222" type="tcp"></server>
 </servers>

  <load>
   <arrivalphase phase="1" duration="1" unit="minute">
    <users maxnumber="100" interarrival="1" unit="second"></users>
   </arrivalphase>
   <user session="xmpp-connection" start_time="1" unit="second"></user>
  </load>

  <!-- JABBER parameters -->
  <!-- to synchronise users,  use a global acknoledgement -->
 <options>
  <option type="ts_jabber" name="global_number" value="100"></option>
  <option type="ts_jabber" name="userid_max" value="200000"></option>
  <option type="ts_jabber" name="domain" value="example.com"></option>
  <option type="ts_jabber" name="username" value="tsung_user"></option>
  <option type="ts_jabber" name="passwd" value="tsung_pwd"></option>
 </options>

  <sessions>
   <session probability="100" name="xmpp-connection" type="ts_jabber">

    <request> <jabber type="connect" ack="no_ack"></jabber> </request>
    <thinktime value="2"></thinktime>

    <transaction name="authenticate">
      <request> <jabber type="auth_sasl" ack="local"></jabber></request>
      <!-- <request> <jabber type="connect" ack="local"></jabber> </request> -->
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      <request> <jabber type="auth_sasl_bind" ack="local"></jabber> </request>
      <!-- <request> <jabber type="auth_sasl_session" ack="local"></jabber> </request> -->
    </transaction>

    <request> <jabber type="presence:initial" ack="global"/> </request>
    <thinktime value="2"></thinktime>

    <transaction name="online">
    <request> <jabber type="chat" ack="global" size="16" destination="online"></jabber> </request>
    </transaction>
    <thinktime value="2"></thinktime>

    <transaction name="close">
      <request> <jabber type="close" ack="no_ack"></jabber> </request>
    </transaction>

  </session>
 </sessions>
</tsung>