Same here (ESP8266 and MicroPython 1.12). When change SSL to noSSL connection, works fine.

I too have this issue using a ublox modem and AWS over TLS. Are there any workarounds?

Same problem, in ESP32 it works perfectly but in ESP8266 it doesn't.

there seems to be some kind of problem when the ssl socket is set to nonblocking and it occasionally returns b"" which results in the OSError(-1). Ignoring it did not help. to work around the problem I created a poll object after the ssl_wrap and in check_msg() I check the poll object instead of mucking around with setblocking(True/False).

YMMV / workaround / not an optimal solution, but it works for me

simple.py

def connect(self, clean_session=True):
    ...
    if self.ssl:
        import ussl
        self.sock = ussl.wrap_socket(self.sock, server_hostname=self.server)
    self.p = uselect.poll()
    self.p.register(self.sock, uselect.POLLIN)    

def check_msg(self):
    #self.sock.settimeout(0.0) #setblocking(False)
     res = self.p.ipoll(0)
     for s,e in res:
        if e & uselect.POLLIN: 
            return self.wait_msg()
     return None   

and comment out the #self.sock.setblocking(True) in get_msg()

According to my test, the problem does not occur because of SSL. The problem is because the server's waiting time is over according to the keepalive=??? My solution is to add a timer that PINGs the server before the keepalive time expires. This solves the problem. Here is a sample code to solve the problem:

from machine import Pin, Timer
from umqtt.simple import MQTTClient
import ujson
import sys
import os

LED = Pin(2, Pin.OUT)
PING_PERIOD   = 120

CHANNEL_TOKEN = 'token_XXXXX'
CHANNEL_NAME  = 'esp32'
RESOURCE_NAME = 'led'
MQTT_SERVER = 'mqtt.beebotte.com'
MQTT_USER = 'token:' + CHANNEL_TOKEN
MQTT_TOPIC = CHANNEL_NAME + '/' + RESOURCE_NAME

def handleTimerInt(timer):
    client.ping()
    print('ping')
    
def callback_func(topic, msg):
    print("topic:",topic," msg:", msg)
    json_data= ujson.loads(msg)
    dt= json_data["data"]
    print("Data:"+str(dt))
    if str(dt) == 'True':
        LED.value(1)
    if str(dt) == 'False':
        LED.value(0)

# create a random MQTT clientID
random_num = int.from_bytes(os.urandom(3), 'little')
mqtt_client_id = bytes('client_'+str(random_num), 'utf-8')

client = MQTTClient(mqtt_client_id, MQTT_SERVER, user=MQTT_USER, password='', keepalive=PING_PERIOD*2  )

myTimer = Timer(0)

try:      
    client.connect()
    myTimer.init(period=PING_PERIOD*1000, mode=Timer.PERIODIC, callback=handleTimerInt)
except Exception as e:
    print('could not connect to MQTT server {}{}'.format(type(e).__name__, e))
    sys.exit()
    
client.set_callback(callback_func)
client.subscribe(MQTT_TOPIC)

while True:
    try:
        client.wait_msg()
    except KeyboardInterrupt:
        print('Ctrl-C pressed...exiting')
        client.disconnect()
        sys.exit()