What we've seen in many cases is startup banks coming to the market with a streamlined onboarding (open your bank account in 5 minutes over videochat), and then

What we've seen in many cases is startup banks coming to the market with a streamlined onboarding (open your bank account in 5 minutes over videochat), and then realizing that many accounts are used for money laundering. They eventually get a warning from the financial authorities and subsequently implement fraud detection algorithms that might be a little too trigger happy, to be on the safe side. It wouldn't be an issue if you could appeal and talk to a human, but challenger banks are, by design, understaffed, and they have no legal obligation to explain why they're terminating your account. However I haven't heard of any bank (proper bank, with a license, challenger or otherwise) keeping your money in such case.