With the update to their client version 5.3.1 for Windows, DynDNS sets the first to entries in your local DNS to 18.104.22.168 and 22.214.171.124. Unfortunately this causes the machine the DynDNS client is installed on to fail to contact any other server within the local network up to giving login issues over RDP if this server is domain joined and requires NLA. The reason is happens is that this update sets the option “Use Dyn Recursive DNS servers on this machine” default.
This can be disabled by opening the client, click Settings, click Preferences and uncheck “Use Dyn Recursive DNS servers on this machine”
Once this option is unchecked, the client will stop hijacking DNS on the machine it’s installed on.