cannot add Mp3 to playlist
I have some Mp3 files in two different folders (they are two different albums). Both ripped in the exact same format (MP3 - MPEG Level 3 Audio) and both at the same bit rite (160 kbps). But in ITunes I cannot add both to a playlist - ITunes will only accept one or the other. If I add one set of MP3s to the playlist, ITunes won't let me add the other, and vice versa. When I attempt to drag and drop, when I try to drop into the ITunes playlist, ITunes puts a little circle/slash icon by the files and won't add them.
Again both file are of the same exact format and bit rate. Why would ITunes do this? (I am using ITunes 12.9.6.3 on Windows 10/64 bit)