It was long expected update, the first cumulative update for Skype for Business Server 2019 has just been released and is now available for download.
You can get it from http://www.microsoft.com/en-us/download/details.aspx?id=58347
The related KB 4470124 listing the installation steps and the issue fixed (yes, just a single issue; don’t know if this because the product has been totally perfect or because it has not been largely deployed yet) is here https://support.microsoft.com/kb/4470124/