FWIW, you can force calculation by selecting them and running GetSizes MD5 or by increasing the size limit in Prefs/Misc/Advanced... But if you're seeing the same thing with just filename+size then the MD5 stuff can't be relevant, so don't worry about that anymore.
[quote]I changed comparison method to filename and size but I still get the same result.
I get the same result each time I click "find" button.[/quote]
Try going up a level from the Duplicate Files results, so you're in coll:// itself, and delete the Duplicate Files collection.
To be sure, fully exit Opus, then open it again and go back to coll:// and verify that the Duplicate Files collection has not come back.
Assuming the collection did not come back by itself, run the duplicate search again (Filename+Size only). Do you get the same results again?