Sorry to hear you’re having problems with your MIDI keyboard. Getting your keyboard to work should be as simple as connecting it to your computer before you run Dorico, then run Dorico. As of the new update, there is an additional option in the Preferences dialog to enable or disable support for MIDI input, so make sure that is set appropriately.
If that doesn’t help, you will need one of my colleagues who knows how to read the various log files written by the VST audio engine to weigh in. Please zip up the VSTAudioEngine_64 folder from %APPDATA%\Steinberg (assuming you’re on Windows) and attach it here, and I’ll ask Ulf to take a look on Monday.