For long or slow copies, it appears the job has hung, as the plugin does not log any messages to indicate it has started copying.
e.g. in one case where i had misconfigured what to copy, and it was copying 10Gb of workspace, the job appeared to just hang. I thought it was a connectivity issue and tried lots of different things. It wasn't until i left it going overnight and the slave eventually ran out of disk space, that the plugin logged it's failure and i realised it had actually been copying files all that time.