This can be due to an unexpected prompt, a command generates no response, or the response includes an unexpected terminator.
Try the following:
- Make sure the prompt received is covered by one of those in listed in your session profile Prompts (More: Terminal>Prompts), or
- Check the Completion attribute of the Step Properties (Telnet Step Defaults> Completion) of the hanging step. In the case of no response, uncheck "Wait for first character before starting idle" and select "Idle" for the Completion Criteria.
If these don't help, use Wireshark to capture packets from a manual session. Use right-hand-mouse click "Follow TCP Stream" "Hex Dump" on one of the responses from your device to view the full conversation.