Here is the best explanation I’ve found so far. This was from an article on Business Insider (I did select to have my fees paid from my refund).
“During the last rollout of stimulus checks in January, the IRS erroneously sent stimulus payments to holding accounts at TurboTax's and H&R Block's partner banks. These accounts are used when a customer opts into refund transfer, meaning they give the company permission to take its fees out of their refund before sending the refund to their bank account.
Both TurboTax and H&R Block said they provided the IRS with the correct bank accounts for customers this time around, so the mishap shouldn't happen again — but it's not guaranteed.
In any case, if a payment bounces back to the IRS then it will be re-sent in the mail as a paper check or prepaid debit card.”
