All bets are off when using a Single Channel Packet Forwarder - they are not supported by TTN as they cause disruption to the network - please disconnect it immediately.
See details here:
It may well be LMIC is getting tied up in knots or even trying different channels - who knows!
We do know LMIC & LMIC-node (the very well supported, tried & tested wrapper for it) works wonderfully on TTGO with a full 8 channel gateway.