So, at around the changeover to the new daily quests and awards, I upgraded a 5 star champion to a 6 star champion. It shows 6 star level 1 in my champion list, but in the battle list, it shows 5 star level 50. I then upgraded skills twice, logged out and back in twice, and it is still the same. 6 star level 1 in champion list, 5 star level 50 in battle list, and when I battle with it, it stays 5 star level 50. But still shows 6 star level 1 in the champion list and 5 star level 50 in the battle list.

EDIT

The problem seems to have fixed itself. I found the champion at its proper rank and level soloing one of the lower stages, so I leveled it up a little bit and then it showed up right everywhere else, it seems.