I farm my 2*; when I get close to level 144 I start stockpiling covers for that character so when I reach 144 I can sell the max champ and immediately roster a new one with multiple covers. I go through the “Claim Your Rewards” screen to select the specific colors I want to apply to the near-max character.
In this instance, I had a level 137 Ares. In my stockpile I had 10 green, 4 red and 8 yellow. The plan was to use 5 green and 2 yellow to get the current one up to 144, sell it, roster a new Ares and make him 5/4/4, then use the two extra yellow to add levels. I went to the “Claim Your Rewards” screen, found the first Green Ares I had and selected “Add Level”. Ares went up a level, I clicked back, and now there was a Green Ares. I thought maybe there were two Greens back to back, so I clicked “Add Level” again. I went back to the rewards screen and the Green Ares was still there. I thought it was a refresh problem, so I found an older one and clicked it. Went back to the rewards screen, Green Ares still there. After this back and forth I eventually got Ares to 144. When I went to roster the new Ares, turns out that one of the Red tokens and three of the Yellow tokens were applied to the previous champ. Luckily I still had enough to max Ares at 5/3/5.
I thought maybe it was a problem with having so many tokens. I had a Hawkeye at 143, so all I had to do was apply one token. I had 2 Blue, 4 Red and 2 Purple stockpiled. I applied one Red. When I rostered the new Hawkeye, turns out it was a Purple that was applied to the champ, not the Red I selected.