Yeah DuckDNS gave me many false positive outages where its resolution failed, for multiple half-days every year I used it (5yrs+).

I moved to the afraid.org and its been solid, if anyone's looking for another free service - only cost is you have to log in once every six months to validate your account is not dormant. They have a paid tier which gives more features (that most home users will never need), and that allows the guy running it to fund a very reliable service.