Don't know what happened, but next time, either split the 2 and leave them split, or select a dual-mono EQ plugin so you can balance the 2 sides with that plugin and keep the original stereo track intact. There's lots of ways to accidentally shift things. I did it today with 4 BGV tracks. I grouped them and tried to copy/paste a chorus to another part of the song. They pasted fine but when I went to nudge them into alignment, only 2 of the 4 regions would move, no matter what I did(all 4 were still highlighted, but they would only move in pairs, upper 2 or lower 2). Things that make you go "Hmmmmmm"
