Welcome to the Lightroom Community. I'll help you figure this out.
Before you make any changes, log on to Lightroom Web (https://lightroom.adobe.com) & ensure everything is synced & backed up correctly. Any unsynced images & edits might be lost in correcting this.
This is a result of manually changing the location of the originals. Did you move the original folder to a different folder on the same drive or an external drive? Lightroom might not recognize changes done externally & as a result, show you what you're seeing. You can go to Preferences > Local Storage > Storage location for originals in Lightroom to set up Lightroom to use a custom location for orignals.