Policy is never to specifically say what caused it. So if you’re hoping for that info, you won’t get it. About the closest you’ll get is PSA: Current Rewards Issues (June 2023) *UPDATED*.
The system looks for unusual behavior. Antifraud doesn’t specify more than that because they don’t want to give any clues on what it might be looking for. Also flags are randomly delayed, so you have no way of testing to see what particular activity gets you flagged. Only thing to know is it sees behaviors or types of patterns that is “irregular” and flags for Brave to investigate. People make tickets and it’s investigated, then decisions are made.