This will never be answered by EA on the forum for legal reasons. Historically only other players discuss it.
From what i saw, there may have been a false auto report on the most recent GAC for Jango finishing with full protection but less than full health or maybe for so many sub 20 seconds battles. Their detection system is unknown for what its detecting. There may have been cheating in game modes that Swgoh.gg doesn't show.
The player is the only one who can go through the appeal and if they didn't cheat the account would be reinstated. EA won't confirm what was the reason.