IPv6 connectivity to mx[1-4].smtp.goog.

Hi, At https://internet.nl we're seeing IPv6 connection issues on TCP port 25 (SMTP) to mx[1-4].smtp.goog. Either 100% DROP (so no TCP connection) or ⅔ failure to setup connection. Further testing seems to confirm the problem is bigger and on Google's side. So, this fails: echo 'quit' | nc -6 -w 3 mx1.smtp.goog. 25 and this works: echo 'quit' | nc -4 -w 3 mx1.smtp.goog. 25 (on MacOS use -G instead of -w) Is anyone else seeing this? Any idea what is causing this? -- Marco