Bug when I sell characters

Sometimes when I sell characters they turn come back on my board but they are red. If I put them in the game my team attacks them and I cant sell the unit or add items to it. If I upgrade the unit to 2 star it will go green 90% of the time and I can sell it but sometimes it will also turn red but 2 star. Please look into this its costing me games by me not having a full board to work with.