Doesn't 1 second of database downtime just mean that a ticket that is scanned during that 1 second window will take 1.5-2 seconds to scan instead of, say, 500ms? Why would that result in 10 minutes of troubleshooting?
These aren't tech savvy people. You don't hire an IT person to stand at a door scanning a thousand QR codes for 20 minutes three nights a week.
Or at the very least the message should tell the operator to retry.
he could build in behavior to retry/wait for several seconds before erroring out but his selling point is speed seemingly (with little risk of sale negatives/positives/theft)