Hello,
Sounds like you are trying to configure a full node RPC adapter and are hitting a firewall.
Firewalls usually cause timeouts and slow down your site.
See the paragraph “When I activate the plugin, my WordPress becomes extremely slow and is unusable.” in the troubleshooting section of the documentation for a short discussion on this.
Generally this is a networking issue. Once you make sure that RPC connections are possible the error should go away.
kind regards