Yes, your rrdcached server. To know which server you use, check out the setting $config['rrdcached'] in config.php
In your case this could be the server where you’ve installed LibreNMS. In my case is a separate server.
in the cron you can add the flush command before the weathermap poller and append a sleep. Or do it like in this post: Weathermap links report "no valid data" with distributed poller (rrdcached)