FTP Voyager Scheduler hangs when connecting to F5

I'm setting up the FTP Voyager Scheduler to download backup files from our F5's. It works on some, with this log message:

[12] Tue 13Oct15 12:05:04 - (Task: f5-internal-01_backup) - Execution successfully completed.

[07] Tue 13Oct15 12:05:07 - SSH_MSG_DISCONNECT: reason code 11; description: Disconnection initiated by user.

But fails on 4 out of 6 with this log message:

The last message is from having to cancel the task, as it just sits at "Executing". The only difference is the F5 OS version, the ones that work are 11.2.0 and the ones that fail are 11.6.0, anyone see this before?