Been seen on occasion in that build. Restart VP and don't load the project, then Go to OPTIONS | DISK tab and Clear Unused Cache Files. Now load the project.
Or use this release for now. Ignore any virus warning. Report back.
Of course, Save Project File AS routinely, giving it a unique # or name, so as not to overwrite prior saves. Using Save Project Files (no AS) will overwrite. From the HOME tab, that choice is available by clicking the caret to the right of the Save Project button on the toolbar. That's your protection.