mqtt client won't connect to broker on same esp8266 (127.0.0.1) about umqttbroker HOT 1 CLOSED

hi,
as I stumbled over the '5x connection and then connection error' issue as well, I've activated lwip <2!
Still no success (but 5+ connections possible) BUT with changing the client connecting from '127.0.0.1' (or "localhost") to the real IP address ('WiFi.localIO()') it works like a charm!
my code now:
[...]
mqtt_client = new MQTT{my_clientID.c_str(), WiFi.localIP().toString().c_str(), 1883};
[...]

Note that I'm using PlatformIO and here activating lwip 1.x one needs to add
build_flags = -DPIO_FRAMEWORK_ARDUINO_LWIP_HIGHER_BANDWIDTH
in platformio.ini
However then build failed in my setup with some 'ipv4_addr_t' being undefined.
I 'fixed' that by adding the typedef myself to
~/.platformio/packages/framework-arduinoespressif8266/tools/sdk/include/ipv4_addr.h
[...]
///////////////////////////////////////////////
#if LWIP_VERSION_MAJOR == 1

#define ipv4_addr ip_addr
typedef struct ip_addr ipv4_addr_t;
[...]

Hope this may help others - cheers, pottendo

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