Because this always happens just after I create a DragonFly release, there’s a new version of OpenSSL. However, this is for version 1.0.2. 1.0.1 is what’s in the release, and it’s supported through the end of the year.
OpenSSH has a major version bump in DragonFly, to 7.3p1. This means some features – specifically patches for High Performance Networking – are no longer there, and you’ll get an error if your config file requires them. Either remove the options from your config, or install OpenSSH from dports.