Aug 20, 2021, 08:3408/20/21
Maybe your champs have the wrong rank. If you want to rank up a champ (for example) from rank 5 to rank 6, you have to sacrifice five other rank 5 champions. In the rank upgrade screen, other champs than (in this example) rank 5 are not even shown.
If you want to rank up a champ from rank 4 to rank 5, you have to sacrifice four other rank 4 champions. Other champs thank rank 4 are not shown.