While troubleshooting our rancher agents (since some nodes are re-connecting all the time, discussion will be another issue) I went through the rancher troubleshooting page where I saw that it still mention the following:
$ docker ps | grep 'rancher/agent-instance'
well on the recent rancher version, there are only rancher/agent and rancher/agent-state, there is no rancher/agent-instance anymore as far as I know.
I guess your documentation needs a real update (beside the visual update which was done recently).
regards