I've been using Poweramp for years now mostly with the same collection of music. I recently purchased and downloaded some new songs and thought I would update my library with those songs. So I transferred them to my phone and then used the rescan library functionin Poweramp. Some of the songs show the album art and tag info, but quite a few of them do not. A lot of the songs in my library show the song title, but no album art and the artist is listed as "unknown artist," and the album is listed as "unknown album."
I'm slightly perplexed, as I verified the tags are correct on