tried different libraries

started with https://github.com/peterhinch/micropython-mqtt.git

then https://github.com/bobveringa/micropython-mqtt.git

but now reverted to umqtt.simple and they all exhibit same behavior

gradually increasing message lenght up to 125 characters, when reached wireshark show multiple retransmits and the publishing stalls

tried with 200ms to 1000ms interval, no difference

!"#$%&'()+,-./0123456789:;<=>?@abcdefghijklmnopqrstuvwxyz[]^_abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'( !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()
!"#$%&'()+,-./0123456789:;<=>?@abcdefghijklmnopqrstuvwxyz[]^abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()* !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()+
!"#$%&'()+,-./0123456789:;<=>?@abcdefghijklmnopqrstuvwxyz[]^abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()*+, !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()+,-
!"#$%&'()+,-./0123456789:;<=>?@abcdefghijklmnopqrstuvwxyz[]^abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()*+,-. !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()+,-./
!"#$%&'()+,-./0123456789:;<=>?@abcdefghijklmnopqrstuvwxyz[]^abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()*+,-./0 this one stalls !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_abcdefghijklmnopqrstuvwxyz{|}~ !"#$%&'()*+,-./01

tested with a socket tcp transfer and i can transmit 20000 bytes without problem