I note the same problem, but I don't know how long ago it stopped. I don't think it was that long, but I can't be sure.
Support discussion has previously told you to use https://wordpress.org/plugins/wp-mail-smtp/ plugin to run tests.
In this case, this is what appear to have broken Jetpack. When it was working, I used this plugin to offload my mail notifications to a 3rd party SMTP server, as my host kept getting blacklisted by other users on the shared server.
Now, if I disable this SMTP plugin, my contact forms work in Jetpack. If it is enabled AND I use SMTP instead of PHP mail() function to send emails, it won't work.
I note that if I enable SMTP plugin and use PHP mail it DOES work.
I also note that when SMTP settings are on a TEST e-mail from the SMTP plugin works fine.
I hope this helps.