Thanks Meirssv for posting a solution. Had the same problem. Funny thing is that TTN only repeats the downlink payload on my LoPy module and not on my Microchip RN2483 module. It's like a downlink handshake from LoPy is missing, so TTN repeats queueing the payload. Can't find any documentation on downlink acknowledgements though. Anyway it works now thanks to your reply.