Please see this thread:

AA accounts restricted (Nov/Dec 2019)

All I know about this is what I learned from reading that thread. I've never heard of anyone getting their account unlocked after it was locked for that reason, and some people were notified that their accounts were locked while others only realized after they tried to use miles they had.

One thing that I gleaned from that thread: It's possible that Citi did one sweep (of other accounts) after they found "suspicious" activity somehow in one person's account.

So what you want to avoid is asking AA to do anything that may cause them to look at your account closely, if you have multiple signup bonuses posting back to back.

Also, if you can sprinkle other earnings (AA Dining, AA Shopping. etc) in between the signup bonuses, it might help. Alaska airlines also did shutdowns, but apparently just for people who only earned signup bonuses back to back with nothing else in between; people who had other Alaska miles earnings in between the signup bonus earnings on their account were not shut down. The more different entries you have in your account between signup bonuses, the less obvious sign-up bonuses being "back to back" will be.