Solution:

Try changing the TCP connection to 4 under the Port 1 Settings because Digi NET+OS has a limited number of sockets. When a socket used for a TCP connection is closed, the socket remains in TCP’s TIMED_WAIT state for a period of time. Repeatedly opening and closing TCP connections at a fast rate can exhaust the operating system imposed limit of available sockets. Setting "number of connections" to >1 is a valid solution, because now there will be an available socket to make the connection to, even if the original (closed) socket is still in the TIMED_WAIT state