This seems to be an bug or something in v4, I still get this a lot myself and cannot work out why as there doesn’t seem to be any uplink retransmissions. here is an example of a modbus controller that reads registers consecutively (RAK7431) each frame counter increases by 1 on each read, but it still displays the UPLINK_F_CNT_RETRANSMISSION occasionally and when it does it seems to display it for a period of time.
i also had this problem with a brand new device added to an application a few days ago (ttgo tbeam mapper - it continually showed the UPLINK_F_CNT_RETRANSMISSION from its first frame uplink after joining and didnt seem to stop, I had to disable the frame counter checks on it in the end).
is this something you have noticed @brocaar there doesnt seem to be any gh issies raised for it yet.
we have more then one gw on our LNS, this node only usually reaches one of them though.
i thought it might of been an issue if it was heard by multiple - but i havent had much spare time to dig into this further yet.