The stashcache authfile generation looks at hostname -f by default. In certain cases (e.g. with LVS), the hostname may not be the FQDN registered in topology, causing the authfile generation to fail.
You can override the hostname that gets looked up by setting either CACHE_FQDN or ORIGIN_FQDN (as appropriate) in the environment when the script is done. This needs to be done as a systemd unit override, as follows\:
For a cache, create /etc/systemd/system/stash-cache-authfile.service.d/override.conf with the contents
For an origin, create /etc/systemd/system/stash-origin-authfile.service.d/override.conf with the contents