We have two services back-to-back on Sundays, one at 9:45a and one at 11:30a. We have several families that serve one and attend one, or serve both. Since reopening post-COVID, we are 100% mobile check-in (of course with a few attended check-in stations). Whenever a family checks into the 11:30 service and had previously checked into the 9:45 service, the labels from the 9:45 service get printed in addition to the new labels they need. This can be really confusing and frustrating for people, just an extra step of sorting through the tags (one family in particular has quite a few check-ins, and they have about 8-10 labels per service). There's a more detailed troubleshooting analysis here.
The default behavior of the QR code is that there is a cookie stored on the person's mobile phone, AttendanceSessionGuids, which is hardcoded to have an expiration of 8 hours.