Many too error_unknown and error_connect_* in log

[1014742868]

Hi,
I am trying to do the load testing of my MQTT Broker using Tsung as client. and publish and spubscribe to topics on the secondary client simultaneously
But there're many error_unknown and error_connect_* in tsung.log, In the node logs we see errors like this:

=ERROR REPORT==== 6-Sep-2020::19:34:26 ===
** State machine <0.2862.0> terminating
** Last message in was {tcp_closed,#Port<0.7674>}
** When State == wait_ack
** Data == {state_rcv,#Port<0.7674>,
{{0,0,0,0},"HP"},
undefined,0,10000,"127.0.0.1",1883,ts_tcp,
{proto_opts,negotiate,negotiate,"/http-bind/",true,
false,false,"/chat","binary",[],10,3,600000,infinity,
infinity,32768,32768,32768,32768,[],true,false},
true,1,
{ts_request,parse,true,[],[],
{mqtt_request,publish,true,10,[],0,[],false,
"topic/%%_random_topic%%",1,1,
"%%_message%%",undefined,undefined},
true,undefined,undefined,undefined},
true,-576460508937400806,-576460733349465560,2,7,true,
-576460508937400806,-576460508937400806,[],<<>>,
{mqtt_session,<<>>,undefined,10,100,4,undefined},
0,1712,524288,524288,
[{loops,100},
{random_topic,<<"zrfvtnkfbp">>},
{message,
<<"ezljenuhjducouiwhmboghrnpfpvijmqvnlyuzfzslvdhfgkwmxtlluzszgnvkklzggyfrnvvnoiiqtokbosilszodxnvozbpdrkwzuikxywsnrcqhksrosoybtmfxcc">>},
{tsung_userid,1712}],
ts_mqtt,[],undefined,none}
** Reason for termination =
** {badarg,[{ts_mqtt,get_message,2,
[{file,"src/tsung/ts_mqtt.erl"},{line,103}]},
{ts_client,handle_next_request,2,
[{file,"src/tsung/ts_client.erl"},{line,816}]},
{gen_fsm,handle_msg,8,[{file,"gen_fsm.erl"},{line,483}]},
{proc_lib,init_p_do_apply,3,[{file,"proc_lib.erl"},{line,247}]}]}

I currently have not a good clue how to reproduce it.
Any help would be greatly appreciated!
The mqtt.xml config like this
mqtt.txt