Created an rsync task with rsync-over-ssh to localhost. ssh keys are set up correctly, and tested from command line.
When I run the task manually, the task exits prematurely, and the only thing I see in /var/log/messages is:
May 1 22:58:42 nassie kernel: pid 27566 (python3.6), uid 0: exited on signal 6 (core dumped)
Another task with rsync modules works fine.