With not that many active users, there should be no need for prolonged delays. Yes every new card company, bank etc has additional checks after all you have to make rules that abide by regulations and your commitments, there still has to be some sort of balance. You are building a rule set based on users, it’s the only way to do it properly.
However, its obvious going wrong if faster payments from established accounts and banks are triggering rules so often with such a low user base.
Also the nature of a new bank account, you transfer money into that account, I’m not sure why that would be seen as high risk, its normal procedure, and it can’t really be justified as because of AML rules, especially if its coming from or to one of the big banks that are very tight on blocking transfers like Barclays for example.