The machines are old, and have a limit on how many transactions we can run before we absolutely have to settle the transactions and close out the machine, before we can reopen it and process more transactions.
When we're settling, we need to maintain a signal the entire time, or we get an error message and have to settle out. On some of the more problematic machines, with the transaction limit hit, it can take upwards of 30-45 minutes from start to finish. And remember, lose the signal for more than maybe a minute, and we get an error and restart.
I remember one trip, I think on 176, the machine hit the limit at Stamford. I desperately tried to get that machine up and running again, but it was down until New London.
Unfortunately...stuff happens. We still try to do our best, given the circumstances.