Comment 1 for bug 1905007

Root cause is at snap.py:
def configure_snap_store_proxy():
    # Do nothing if we don't have kernel support yet
    if not kernel_supported():
        return

    if not reactive.is_flag_set('config.changed.snap_proxy_url'):
        return
    ensure_snapd_min_version('2.30')
    snap_store_proxy_url = hookenv.config()['snap_proxy_url']
    if snap_store_proxy_url:
        bundle, store_id = download_assertion_bundle(snap_store_proxy_url)
        try:
            subprocess.check_output(
                ['snap', 'ack', bundle],
                stdin=subprocess.DEVNULL,
                universal_newlines=True,
            )
        except subprocess.CalledProcessError as e:
            raise InvalidBundleError(
                'snapd could not ack the proxy assertion: ' + e.output)
    else:
        store_id = '' # THIS OVERWRITES THE STORE ID IF IT IS SET