Its is working now... but intermittently...
If anyone else has this problem: I re-did the wiring. I had checked the connections a gazillion times, and everything seemed in proper order. I decided to re-do the wiring and this time separated the jumper wires from each other.
After a restart, the gateway worked for about half an hour and then stopped with the following message:
ERROR: [main] unintended SX1301 reset detected, terminating packet forwarder.
Not sure what this one is!