This is not a bug…
LoRaWAN Frames are only for debugging purposes.
Transporting MAC commands and application payloads in FRMPayload (encrypted data)the field.
The device data tab shows actual device application data.
Device Data which is base64 encoded is not random it’s the actual data payload sent by your device.
LoRaWAN® Specification v1.0.3 - LoRa Alliance® (lora-alliance.org)