Lacking much detail in your question, some more random thoughts to consider:
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If the device is using ABP, and has been restarted when moving from one location to another but does not persist its LoRaWAN state (that is: if the frame counters started at zero again): see ABP node stopped working -> Fixed by creating new ABP.. Why? :)
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If you’re using different accounts, then see “Collaborators” in your application’s Settings in TTN Console.