Her racist tweets towards Zayn Malik are likely the cause.
Azealia Banks is known to be pretty controversial on Twitter, but this week, she crossed the line when she decided to attack pop star Zayn Malik with racial slurs, which is likely the reason her Twitter account is not accessible today. If you visit Azealia's page, you'll be greeted with the message, "The account you're trying to view has been suspended," an action Twitter generally takes when someone has been reported for violating their guidelines.
Her offensive tweets at Zayn, as well as her subsequent berating of 14-year-old Skai Jackson who came to his defense, have also led to her removal from the lineup of U.K. festival Born & Bred.
BallerAlert also points to the tweets she sent out just before her account was suspended, in which she referred top "Whiteness" as a mental illness. She also says she's cancelling her shows and "going away". See those tweets below.