Most of the time there’s one reason: NFC is turned off on the phone. It takes ten seconds to turn it on.
There’s a workaround: the staff have a single-scan QR pass. Point your camera at it and you’re in the room, no tag needed.
Go to the staff and ask them to show you the QR pass to the room.
The tag confirms that you’re here. That’s why only people nearby are in the room.