umqtt.simple cannot transmit longer messages than 125 ascii characters on Pico1 W

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

Start by reproducing the length threshold with umqtt.simple on the Pico1 W and inspect the publish traffic in Wireshark. Compare the failing MQTT behavior with the reported socket TCP transfer and the peterhinch/micropython-mqtt and bobveringa/micropython-mqtt implementations. Done means identifying and fixing the cause so longer ASCII messages publish without retransmits or stalling.