Probably an issue with your configuration settings. In a quick and dirty test (WAN DNS fields set to CloudFlare) of a single no-ip.com free account I've had for ages I don't seem or appear to have a warning indicator (exclamation point) when I enable DDNS and input my no-ip info.Yes ... I use www.no-ip.com.

DDNS Router Setup Guide: Learn How to Configure DDNS
Learn how to configure DDNS in a router by clicking through to this helpful Knowledge Base article.

How to Setup DDNS in an ASUS Router - Support | No-IP Knowledge Base
If you have a Asus Router with Firmware 3.0.0.4.220 or above you can now use its embedded DDNS client to update your No-IP.com hostname.

How to Setup DDNS in an ASUS Router - Support | No-IP Knowledge Base
If you have a Asus Router with Firmware 3.0.0.4.220 or above you can now use its embedded DDNS client to update your No-IP.com hostname.