I have had and endless set of issues with Cubase 12x. The only thing I can do to get things stabilized is to delete this folder: C:\Users\xx\AppData\Roaming\Steinberg\Cubase 12_64
When I do that and re-start, Cubase re-creates the folder and I can session for a while. Once I run into any issue (previously posted - eg: quit bug, vsti load bug ), Cubase 12x will no longer quit or load properly. In order to get back to a workable platform I have to delete this folder. It stays stable for some time (I cannot quantity) and then once it starts acting up again I have to repeat the process.