ejabberd: XML stanza not acknowledged - xmpp

Question

While resuming a stream managed session of ejabberd, I get the below logs:
2016-04-11 08:53:07.430 [info] <0.5432.11>#ejabberd_c2s:terminate:1752 Closing former stream of resumed session for 54ff31587261691606060000#108.59.83.204/sender
2016-04-11 08:53:07.430 [info] <0.7868.11>#ejabberd_c2s:handle_unacked_stanzas:2814 1 stanzas were not acknowledged by 54ff31587261691606060000#108.59.83.204/sender
2016-04-11 08:53:07.430 [info] <0.7868.11>#ejabberd_c2s:handle_resume:2731 Resumed session for 54ff31587261691606060000#108.59.83.204/sender
2016-04-11 08:53:08.602 [info] <0.8227.11>#ejabberd_c2s:handle_enable:2644 Stream management with resumption enabled for 5695b87d7261697179130000#108.59.83.204/sender
2016-04-11 08:53:09.516 [info] <0.8227.11>#ejabberd_c2s:terminate:1779 ({socket_state,gen_tcp,#Port<0.138899>,<0.8244.11>}) Close session for 5695b87d7261697179130000#108.59.83.204/sender
2016-04-11 08:53:09.517 [info] <0.8227.11>#ejabberd_c2s:handle_unacked_stanzas:2814 1 stanzas were not acknowledged by 5695b87d7261697179130000#108.59.83.204/sender
2016-04-11 08:53:09.987 [info] <0.458.0>#ejabberd_listener:accept:333 (#Port<0.138210>) Accepted connection 106.196.172.221:58035 -> 10.240.0.3:5222
2016-04-11 08:53:11.157 [info] <0.8254.11>#ejabberd_c2s:wait_for_sasl_response:919 ({socket_state,gen_tcp,#Port<0.138210>,<0.8185.11>}) Accepted authentication for 5695b87d7261697179130000 by undefined from 106.196.172.221
Here 1 stanza was not acknowledged, what does it mean and how to correct it.
Sometimes, few delivery acknowledgements are not received by the receiver client, is this the reason that those stanzas are getting lost?
UPDATE:
Stanzas not acknowledged during a session are exchanged again when the connection resumes. But there are cases when some stanzas are getting lost, as a result delivery acknowledgements are not reflected on the sender client side.
Parameters set for stream management:
Resume on timeout: 120 seconds
Resend on timeout: true
Is there any configuration that I may be missing due to which some stanzas are getting lost?

Answer 1

It means that you are using stream management and that your client did not confirm he received some stanzas. If this were messages they will be stored for offline delivery or resend on another connections, so you should not lose any message.