Seen that blog! This is the mod I did. Indeed. Lets get the metal cover off and find the Low Noise Amplifier (LNA).
The gateway was functioning perfectly up to the last second just before I started sending with 18.5dBm (so the node was sending. I also switched off the over current protection in the node). Since then, the gateway stopped receiving (-40dBm).
I totally agree it is unlikely that this broke the gateway, because to much distance (reception <10dBm)
May be it’s just bad luck somehow. About the dummyload/power meter on the lora node: even more unlikely that it has damaged the gateway.
Anyway, its broken and I will start looking for the circuitry. Will be very challenging without a schematic diagram.
Thanks all for your replies!