Uncertainity with CIPSEND command to updating the data field on thingspeak using esp8266
Apparently the length of your data:

GET https://api.thingspeak.com/update?api_key=U6PE1HI433A8XPQY&amp;field1=46


is 72 characters, plus \r\n\r\n makes exactly 76 characters. I guess if you specify a longer length in CIPSEND it is expecting more data, and you are being disconnected due to a timeout or something.