Fatal exception 3(LoadStoreErrorCause) with NodeMCU

[artwebstudios]

I got the following error trying to send a MQTT Message with NodeMCU to AWS IoT:
Fatal exception 3(LoadStoreErrorCause):
epc1=0x4020d7b1, epc2=0x00000000, epc3=0x00000000, excvaddr=0x40000000, depc=0x00
Panic /Users/arodes/Library/Arduino15/packages/esp8266/hardware/esp8266/2.4.2/cores/esp8266/core_esp8266_main.cpp:134 loop_task

I want to send MQTT message with several MAC address like this:
//send a message
char buf[100];
strcpy(buf, "{"MAC":["08:d5:9d:63:3b:fe","44:f4:36:e0:30:a8","48:ba:4e:16:c0:09","78:4f:43:5e:de:ee","48:ba:4e:16:c0:08","1c:b0:44:38:19:4f","84:f3:eb:b4:50:23","08:d5:9d:63:3b:fc","24:5e:be:1f:0f:fb","b4:8b:19:c7:37:8a","68:d9:3c:86:8f:fa","08:d5:9d:63:3b:fd","70:c9:4e:00:01:0b"],"RSSI":[]}");
int rc = client.publish(aws_topic, buf);

Any idea??