From my experience in cross border payments, sanctions screening (Office of Foreign Asset Control - OFAC) is the most likely source of the problem. Most likely, your customer's bank uses a US bank as a correspondent for all of their USD payments. The correspondent bank will scan every payment instruction that they receive against a list issued by OFAC. If there is a match, the correspondent bank will not execute the payment, and will seize the money from your customer's bank's account with the correspondent. In order to get the money un-seized, your customer will need to provide his bank with a lot of documentation proving that he is not the bad guy on the OFAC list. This can take a while. Your customer is probably aware of all of this and that is why he is not hassling you.

So yes, the banking system did eat his money, but that is what it is designed to do.