This question comes up from planners who have thought about it properly, and it deserves a real answer rather than reassurance. If two security staff are scanning at two different gates and both phones have lost network, what actually happens?
The short version: each gate keeps working perfectly on its own, and the two gates cannot see each other until they reconnect.
What still works
Each phone holds your full guest list from the moment you prepared the event on it. So each one can verify any code, admit any valid guest, and refuse any code it has already scanned itself. Nothing about a gate stops functioning because the network dropped.
Every scan is stored on the device and uploads to your dashboard as soon as a connection comes back. Nothing is lost.
What does not work
Gate A has no way to tell Gate B what it has just scanned. There is no connection between them to carry that information.
So if someone forwards their code to a friend, and one of them presents it at Gate A while the other presents it at Gate B, and both gates are offline at that moment, both will be admitted. Each phone checks its own record, finds nothing, and shows green.
When the phones reconnect, the system keeps the first check-in to reach the server and marks the second as a duplicate. You will see it in your record. But it is caught after the fact, not stopped at the door.
How likely is this actually
It needs three things at once. Someone has to deliberately share a code, two people have to arrive at two different gates within the same window, and both gates have to be offline at that moment. At a single gate event it cannot happen at all.
Uncommon is not impossible though, and if you are running a five hundred guest event at a venue with bad signal, you should know about it in advance rather than read about it in your report afterwards.
How to plan around it
Keep one gate online. Put your most reliable phone with the strongest mobile data on your main gate. If a code looks doubtful anywhere, send that guest to the online gate where the check is against the live record.
Check venue signal before the day. Stand at the actual gate position with the phone you will use. Reception at the entrance of a hall is often very different from reception in the car park.
Watch your dashboard as gates reconnect. Any duplicate that got through will surface there. At most events this list is empty, and if it is not, you want to know while people are still in the room.
Single gate events need none of this. One phone sees everything it has scanned. Offline changes nothing for you.
Why we are telling you this
Because you will find out either way, and finding out during your own event is worse. Any platform that tells you offline duplicate blocking works perfectly across separate gates is either not being straight with you or has not thought about it.
We would rather you plan your gates knowing exactly what the system does and does not do. That is a better outcome for your event than a claim that sounds cleaner in a sales page.