As part of the Active Directory joining process, an automatic update of the related DNS server is attempted by adding a new A record for the host being domain-joined. If this is not possible, the Active Directory join still succeeds, but a warning is issued. This warning looks as follows and simply states that the domain join was successful, but the dynamic DNS updating step after that had failed.
The cause for this behaviour is often that the DNS Server is set not to allow "Dynamic updates" (as seen in the image below), and/or the DNS server is intentionally statically managed.
To update the DNS server manually, simply add an A record for the Canary's IP. If the fully qualified domain name is corp.thinkst.com and the Canary's name is srv01, create an A record that points srv01.corp.thinkst.com to the Canary's IP address.