Missing photos are duplicate files which cannot be linked to their source photo

LR Classic seems to be creating duplicate photos which are then found in 'missing photos'. When I try to link them to the proper source file, an error message says it is already linked to another photo in my catalog. This must be some bug in LRC; how do I fix it?

LRC finds 226 missing photos. I highlight one of the photos and select Show In Finder, then click to locate the file (see screen shot 1). I then navigate to where the file is, and click to select it (see screen shot 2). But there is an error message that this file is already associated with another photo in my catalog (see screen shot 3). Screen shot 4 shows the collection the photo is in.

So my question is why is there a missing photo with the same name as this one that is properly linked to the reference file? How do I find out what category(ies) this missing photo is located in? Do I dare just delete this missing photo which seems to be a duplicate? How did it get created? How can I prevent this happening in the future? This seems dangerous to just delete a photo from the catalog like this.