The mix of "ft." "," and "&" makes things a little wonky. Do you have any of these characters set to split multiple artists?
If the affected songs and the albums containing them are all located in one "artist" folder that's easily movable, I suggest moving it to somewhere outside of Poweramp's view, rescanning your library (so they disappear), then before moving the "artist" folder back, add an underscore to the folder name (so it appears totally new to Poweramp). Then move the folder back and have Poweramp rescan your library again.
If you haven't done a full rescan yet, that should be the nuclear option that ought to fix it if all else fails.