Two Downlinks with no payload immediately after Join

Hey folks!

Set up my first gateway and node in Philadelphia today!

All is going well with sending basic “hello world” uplinks, but I’m hitting one oddity. Immediately after the node performs a successful join, the first two uplinks are each followed by a zero-byte downlink. After that, the node continues to send unconfirmed uplinks as expected.

I’m using the standard ttn-otaa code from LMIC, on a Adafruit Feather 32u4 (RFM95 radio).

Does anyone know what these downlinks are?

14%20AM