The most likely issue is that the configured timeouts on the reverse proxy are too low.
If you set up your Artemis instance with the Ansible Role (>=v0.1.1), you can set the timeout values with the following variables:
proxy_send_timeout: "900s"
proxy_read_timeout: "900s"
fastcgi_send_timeout: "900s"
fastcgi_read_timeout: "900s"If you configured the nginx reverse proxy by hand, you have to adapt the following variables in your nginx configurations: