This a "Connect/receive error". It can also be protocol problem, such as "not enough data sent".
Possible work-arounds / solutions: increase timeout value or number of attempts.
typedef enum BackStatusCode {
STATUSCODE_INVALID = -1,
STATUSCODE_TIMEOUT = -2,
STATUSCODE_SLOW = -3,
STATUSCODE_CONNERROR = -4,
STATUSCODE_NON_FATAL = -5,
STATUSCODE_SSL_HANDSHAKE = -6,
STATUSCODE_TOO_BIG = -7,
STATUSCODE_TEST_OK = -10
} BackStatusCode;