Mine still fine, even after i once got total ban (you stuck at loading) and shadow ban.Looks like bans are IP related
My account names were: Polar, Artic, Sargatanas, DoomLord, Gaia and AniviaMain.
All banned, two of them were not even used (Only finished tutorial on them)
So looks like they know who is the owner of the accounts, no matter the name or if they look legit; I got banned in my lv120 account after almost 5 months of dense gameplay just because i spent 5000 gems in dragons i didnt had
Just tested and fine. Detecting modified apk is easy and can be done in a lot of ways, so they probably check if you were using original or modified apk.
Even if you didn't enable any hack option, as long the apk were modified, they already detect you.