Ideally you'll enable the ssh service on the "remote" Mac and run rsync in proper client/server fashion. This is far far more efficient than mounting a remote filesystem.
Nevertheless, let's assume you're still mounting the remote filesystem. Simplify the command and see what's happening here. I've removed -z because it's ignored when copying between directory points that appear to be in the local filesystem, and added -v to see what's going on. You might need to add another -v to get additional output
rsync -av /Volumes/henry/* /Users/home_henry_from_astro/
You've copied 800+ GB of data already. The rsync process has to skip all of that. Now because you've used the -a (archive) flag it can skip files based on size and time. But it has to retransfer in entirelyentirety any file that has either a different size or timestamp. Not just the parts that are changed, but the entire file. If this is a large file it's going to take quite a while to copy. (This is where you can gain if you can run one rsync on each end of a network connection, as then only changed blocks need to be retransferred.) If you're watching, you can use the --progress flag to see what's going on, but don't use this flag if you're writing to a log file
rsync -av --progress /Volumes/henry/* /Users/home_henry_from_astro/