About 10 years ago I looked into creating my own ACH system so I wouldn't have to use an intermediary (this was because I was going to be doing high dollar, low quantity transactions).
Because I was going to be setting up an import operation, I wanted to understand what my liabilities might be if a customer either didn't actually have funds in their account or they were fraudulent.
A key concern was the amount of time my company would be liable for the funds transferred to it, because even a single reversal would cause a serious problem for the company.
I learned that the receiving institution can initiate a reversal, and there is no time limit to establish when they can no longer do this. So, theoretically, they could just reverse all transactions for a year, or however long, and my company is on the hook for all of this cash.
Worse, my institution is what's actually on the hook, because they automatically send the money that the reversal is requiring. It seems you are doing a more technical analysis, but the issue comes that if you are a small business unable to deposit $1,000,000 in a CD as a security against such misfortunes, then you are locked out of getting such a service.
Or at least this was the case ~10 years ago.