Pretty new to Jenkins and I have simple yet annoying problem. When I run job (Build) on Jenkins I am triggering ruby command to execute my test script.
Make sure your script is flushing its stdout and stderr.
In my case I had a buffering issue similar to what you describe but I was using python.
The following python code fixed it for me:
import sys
sys.stdout.flush()
I'm not a Ruby coder, but Google reveals the following: