Try enabling the dump_log which shows the hex characters. It could be how and where newlines are sent. They could be \r\n, \r, \n and you'll see this as hex 13 and 10 in the dump_log. Sometimes the prompt starts with a newline so you'll need to make sure the correct character is matched at the beginning. I'll admit I've had frustrations with this as well using Net::Telnet::Cisco way back when connecting to IOS-XR switches.