You'll get the same treatment with the anti-fraud/kyc team at any bank. It's standard procedure to not disclose reasoning because it essentially helps fraudster

You'll get the same treatment with the anti-fraud/kyc team at any bank. It's standard procedure to not disclose reasoning because it essentially helps fraudsters/criminals avoid checks. There can also be legal restrictions on what they can tell you. For example if they think you're committing money laundering it can be a criminal offence ("tipping off") for them to tell you that why they're investigating you. It might also not even be directly about your business, if for example one of your counter-parties (customer/supplier) is subject to criminal investigation it could result in you getting flagged up as a related party. It sucks when it happens but unfortunately it's a reality at every bank.