Thanks, Sil.
Some good ideas, but if I remove any plugins from the project, the problem goes away! So it’s not an informative test.
The problem is some kind of “artificial” resource barrier, somewhere.
Also, removing, say, the VST3 plugins from the VST folder would do nothing if I’m not using the plugin. That troubleshooting step only helps if either Cubase is having issue validating the plugin, or if it’s being used in the project.
32-bit J-Bridge. It’s not a bad idea. I did think of that. I’m just not sure I’m ready to take a step backwards in time like that.
And, I never even install the 32-bit version of plugins anymore. 
I think that’s a ship I’m going to have to let sail away.