There are others with similar SSH errors from the last day or so:
- :nxdomain errors when connecting to Postgres after upgrade - #5 by sax
- Could not translate host name "top1.nearest.of.***.internal" to address: Name or service not known
Several months ago a similar issue was described here, they mention that the logs (flyctl logs) contained some more information and that SSH worked after completely removing the app and launching+deploying it again.
There was also another similar issue a couple of months (SSH Handshake Failed) which was resolved internally.