Updated 14 November 2019: This issue is now resolved. Please read on for more information.
Since Catalina’s public release on 7 October, a number of Dorico 3 users who have updated to Catalina are experiencing problems related to the VST audio engine. Not all users are experiencing these problems, and not all users who are experiencing problems are experiencing all of these problems, but we believe the problems are common enough that we are issuing this advisory to try to make users who are considering upgrading their Macs to Catalina aware that they too may experience problems. These problems have also been reported by a small number of users running Mojave.
The problem was caused by a bug in the eLicenser subsystem, affecting the Soft-eLicenser. As of the release of eLicenser Control Center 220.127.116.1159, this bug is now solved.
The symptoms are typically that Dorico will hang when performing operations that require communication with the VST audio engine, because it has already crashed in the background, and Dorico is therefore left waiting for a reply that does not come. These operations including saving the project, auto-save, playing back, and exporting audio. Because the VST audio engine is a separate process to Dorico itself and does not present any user interface beyond displaying VST instrument and effect windows, there is no visible sign that the audio engine has crashed.