From another user:
"The issue is they added a ton of automation lanes to VE Pro that means cubase auto creates all these auto lanes per return lane from an instance. So say you have 130 return stereo lanes, each one in the Cubase mixer now creates 20 auto lanes too. So now you have the Cubase mixer trying to create 2,860 mixer lanes every time it tries to open a session instead of 130. And there's no way around this with the VST3 standard -- if the plugin presents auto lanes they will be created in the DAW mixer."