So I used socket, transmission rate 1 per sec
Data transmit, 80 bytes
After a few minutes, about 4min, this "error" or whatever it is, appeared and it countiously spammed on the REPL for like every second.
esp.freemem() --> 16208
I'm using the last micropython esp8266 firmware
Same with the esp-open-sdk

The code:
while True:
... s=socket.socket(socket.AF_INET,socket.SOCK_STREAM)
... try:
... ... s.connect(('TCP_IP',TCP_PORT))
... ... print('connected')
... ... pin.high()
... ... s.send('ping')
... ... data=s.recv(80)
... except:
... ... break
... while sig==0
... ... kom()
... sig=0
... pin.low()
... pyb.delay(1000)
... gc.collect()

kom() is function for i2c communication, no big deal, just sending some data