So u didn't format data after flashing the romI did actually. My steps were:
1. Flash A11 via Recovery.
2. Format data > Yes
3. Flash AEX
These were the steps I did for just Vanilla.install, no Gapps. And contrary to what TaimoorBoss said, that I should flash Gapps, that's wrong. Android Setup should not crash on a Vanilla build even with or without Gapps.
It's weird. I got frustrated and decided to go try crDroid again and that flashed without a problem. I'll stick with crDroid for now.
AEX has been solid stable though. I was running the last build since it released and I never considered switching ROM until the update messed up. The maintainer of AEX is very nice too. Hoping to go back again after a few more updates.