This happened to me where 2 characters passed level 10 in quest mode but I lost the scenario, so it gave me the XP, but skipped the rewards. Luckily, when I went back and looked at the character screen, it looked like it doubled an older version of the 2 characters at level 8, so I was able to take those older 2 and replay them. I don't know if the copying of those 2 characters was a result (or cause?) of the bug, but it wasn't anything I had done on purpose.