We’ll need many more details.
In TTN Console:
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Did you delete the devices from the application before you deleted the old application?
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Did deleting the application give you any warning about the existing devices?
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Which of the details are the same as in the previous registration: DevEUI, AppEUI and/or AppKey?
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Did registering the devices in the new application give you any warning/error about an existing DevEUI?
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Does clicking the OTAA Join Requests in the gateway’s Traffic page (orange icons) give you any more details about what might have gone wrong?
And as for the devices:
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Did you change anything in the devices?
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Can you program the devices yourself? (Like to change the AppEUI, AppKey or even the DevEUI.)
Related: How can I reuse hardcoded AppEUI and AppKey after I deleted an application?