TLJH always serves /hub/ regardless of parameter in config.yaml

I am running a TLJH server on Ubuntu 20.04.3 LTS (Focal Fossa). I would like the login to be available at a path on a subdomain I own, After searching for a while, I know that I should be able to do this with sudo tljh-config set base_url /jupyter and then sudo tljh-config reload proxy. Doing this makes sudo tljh-config show show correctly that the config.yaml file has been changed, but upon inspection, nothing in the traefik rules.toml has been updated (that is, the file still looks like)

rule = "PathPrefix:/"
data = "{\"hub\": true}"

What’s going on here? Any workarounds?