After migrating from chirpstack v3 to v4 all the devices and gateway got migrated, But the issue is that the devices are not able to get the data from Lorawan devices. On restarting the gateway we were able to get the data from the devices.
Is there a way where can achieve this without restarting the Gateway Devices.?
The migration tool does migrate the device-sessions (if you are using the correct parameters of course), so devices should remain active.
On restarting the gateway we were able to get the data from the devices
This sounds that the issue might have been with the gateway, e.g. still pointing to your v3 environment, not v4. If this is the case then the device-sessions were correctly migrated, only the data was forwarded to the wrong end.