Kstewart got it. There is a Basics Station gateway in the QA lab on the floor above, registered in our org by the QA team. That’s what heard my “sporadic” frames, my dev kit board never forwarded a single one. Borrowed it for the bench, removed the single-channel board, removed the channel hack. Joins first time, uplinks every 60 s on all eight channels. The 868.1 trick did work in between, for the record.