Rclone takes 18 minutes to start copying then uses 8GB+ of memory

That looks like it is still listing the directory which is not what I was expecting from my tests. When I try the test I don’t see any list directories happening.

Can you check the version of your rclone beta for me? /usr/sbin/rclonebeta version ? You need to be using at least v1.44-006-gc5ac96e9-beta but preferably the latest.

What you can do is add -vv --dump headers and this will show the http transactions in the log- that will give you a clue as to what is going on.