•   Inability to complete KYC or provision of wrong data for KYC
• Non compliance to the rules of trade or P2P
•   If the law enforcement agents demand so
• If the exchange decides to do so without any reasons
• Use of tilted coins
• Loggin in your account with frequently chnaging IP address and etc

Those points and more is given not based on the story of your US based friend. Not your key, Not your coin. They can freeze your fund anytime without your permission.