Finder and Spotlight not returning the expected results when searching
Fixed!.  I just rebuilt the spotlight index like this:
System preferences > Spotlight > Privacy, add and then remove the folder that wasn't returning the expected results (I did it with the home folder just to make sure all is indexed), after you quit System preferences the index will rebuild for that folder.  I guess you need to wait a bit for macOS to rebuild (5 minutes, 1 hour or more? I don't know, it surely depends on the size of the folder).