Repeating songs after I load albums. Please help

“The duplicate files have a “sid” extension. From what I can tell they don’t serve any purpose. I just delete them.”

In File Explorer, the duplicate files aren’t there, so can’t tell what file extension they have.

Deleting songs on the MP3 player would be a huge hassle, as there are dozens – hundreds – of them.

How are the duplicates kept from happening in the first place.