I have a deck that revolves around the affinity from witherbloom, the balancer discounting hybrid mana spells to free (namely rakshasa's bargain). however, at any point where I have 6 creatures and should be able to cast the spell for free, arena does not recognize it as a spell i can cast from my hand and it auto-passes through the turn (unless in full control, in which case I can cast the spell from my hand even though it is not highlighted as an action i can take). this takes place on both mac and ios, and presumably other platforms. i will continue to play in full control for now, but would love for this to be fixed :D