I encountered this really weird bug where the attack multiplier (+20%) wasn’t being applied to heroes even though I had not used them before on the mystic titan.
I selected a team, exited the screen to do something else and pressed “save team” as I did so, so I could use it later. Now these heroes simply do not have a multiplier mark on them.
My hits also were quite low after I used them, and the multiplier did not change. So these heroes are basically broken for good, the score multiplier is not affected no matter how often I use these heroes.