1: The financial institution could have a technical issue, such as it's systems are down or aren't working properly
We can compare this technical issue with the delay that your friend might experience if the sender or you've paid for the lowest fee ever. It has been a problem of other newbies that they only pay for the lowest when the network is congested which results to the delay of the sent payment.
2: The transfer limits for your or your friends account could have exceeded
There is a central point of failure: The bank
Although the comparison that I'll tell isn't that much to compare but on the other hand, we also got limits in exchanges but not in wallets we use.