This seems similar, although not identical to the issue I have seen with versions newer than 3689: Error running Verify Setlist report on ver 3693. In my case, the issue appeared when trying to an Embedded Rack containing an instance of Omnisphere. If I replaced that Embedded Rack with just the Omnisphere VST, the error went away.
The error was only in the Verify Set List functionality, not in the usage of the plugin or rack. I would call it a minor bug because of that, but maybe something @brad could look into at some point. Maybe something in the way that Verify Set List logic parses the Embedded Rack?