Have not experienced the services instability but had problems installing Lets Encrypt SSL, have switched to paid basic RapidSSL and it works with TLS 1.3, but although installed using the SSL configurator, there is a problem with the intermediate cert which is not appearing in the chain, even though it is installed. But SSL is working OK for me - using Ubuntu 16.04, just needs the intermediate cert to work properly.

18th Jan 2020: SSL works on mono with version 19.6!

from the release notes:

Updated Mono support for Linux on-premises installations

We've updated the Mono architecture that's used for our Linux on-premises installers.This fixes many security issues such as TLS 1.0 limitations, and it helps us keep Mono up-to-date in the future.

We officially support these Linux distributions:

• Ubuntu 64-bit LTS
• Debian 64-bit (latest stable release)

Thank you!

So version 19.5.25995.7276 is out. 

Has Mono been updated as per this email from 19th August 2019:

We’re upgrading Mono for increased Linux security and sustainability. The updates will add support for more recent versions of TLS as well as a greater number of 64-bit Linux distros. You will also notice a general improvement in performance when connected to a large number of sessions.

Does this version now support TLS 1.3? 

It doesn't appear so. When will the upgrade to Mono be available? It would be really nice to know what is happening with this issue.

Thank you

You've been promising for months that 19.4 will contain the updates to Mono. I just updated to 19.4 and like the others above i find it's still using TLS 1.0. And now you say "should be available soon"  When???

This is really frustrating!!!!  Why do you promise something that people are waiting for and then not deliver???