Diagnosing unreliable join-accept reception

Further, @Maj reported in October last year that v33 and LBT broke downlinks for him. So in summary…

| MTAC-LORA-1.0     | Downlinks broken on AS923 |
| MTAC-LORA-1.5 v31 | Works with LBT disabled   |
| MTAC-LORA-1.5 v33 | Downlinks broken on AS923 |

??