I have recently migrated from LR CC to Classic. I didn't turn off sync. Now classic only shows smart previews and the original 'not found'. I tried downloading originals using downloader but only got the smart previews. And way to recover them?
We're sorry about the trouble. Would you mind telling us how and from where did you download the originals? Do you see any exclamation marks on the images in the upper right-hand corner in the grid view? Is it possible if you can share the screenshot of the Lightroom Classic with the Library module selected and the folder section on the left-hand side?
Please go to Edit > Preferences > Performance tab and see if "Use Smart Preview instead of Originals for image editing" is checked or not. If it is checked then, uncheck that option and see if that helps.