My issue is that no sensor nodes are found in Ethernet gateway configuration, while in serial gateway configuration everything is working.

@Yveaux
In Ethernet gateway mode, resetting sensor nodes didin't help.

Not sure it's Domoticz, because the same Pi with the same radio plugged into an Arduino in serial gateway mode produces lines like below for all sensor nodes, without even resetting anything:

cat /dev/ttyUSB0
0;255;3;0;9;241037 TSF:MSG:READ,20-20-0,s=7,c=1,t=0,pt=7,l=5,sg=0:24.4
20;7;1;0;0;24.4
0;255;3;0;9;241135 TSF:MSG:READ,20-20-0,s=8,c=1,t=1,pt=7,l=5,sg=0:46.1
20;8;1;0;1;46.1
0;255;3;0;9;241229 TSF:MSG:READ,20-20-0,s=255,c=3,t=0,pt=1,l=1,sg=0:93
0;255;3;0;9;241236 TSF:MSG:ACK REQ

@Yveaux Should I try with a different controller? If so, which one would you recommend?

My issue is that no sensor nodes are found in Ethernet gateway configuration, while in serial gateway configuration everything is working.

My configuration:
Raspberry Pi 4B, Ethernet gateway, RFM95

This radio works in the serial gateway configuration with an Arduino board, being connected to the same Pi / Domoticz through USB, all sensor nodes are listed as they should.

If I connect the very same radio unit directly to Pi in Ethernet gateway mode, Domoticz sees the gateway and puts the following into the log.

• From Domoticz log:

2021-06-22 21:11:58.154 Status: LOCAL_GW: connected to: 127.0.0.1:5003
2021-06-22 21:12:00.573 LOCAL_GW: Gateway Ready...
2021-06-22 21:12:00.574 LOCAL_GW: Gateway Version: 2.3.2 

• mysgw output

$ sudo MySensors/bin/mysgw 
Jun 22 21:11:53 INFO  Starting gateway...
Jun 22 21:11:53 INFO  Protocol version - 2.3.2
Jun 22 21:11:53 DEBUG MCO:BGN:INIT GW,CP=RLNGL---,FQ=NA,REL=255,VER=2.3.2
Jun 22 21:11:53 DEBUG TSF:LRT:OK
Jun 22 21:11:53 DEBUG TSM:INIT
Jun 22 21:11:53 DEBUG TSF:WUR:MS=0
Jun 22 21:11:53 DEBUG TSM:INIT:TSP OK
Jun 22 21:11:53 DEBUG TSM:INIT:GW MODE
Jun 22 21:11:53 DEBUG TSM:READY:ID=0,PAR=0,DIS=0
Jun 22 21:11:53 DEBUG MCO:REG:NOT NEEDED
Jun 22 21:11:53 DEBUG Listening for connections on ???:5003
Jun 22 21:11:53 DEBUG MCO:BGN:STP
Jun 22 21:11:53 DEBUG MCO:BGN:INIT OK,TSP=1
Jun 22 21:11:53 DEBUG TSM:READY:NWD REQ
Jun 22 21:12:00 DEBUG ?TSF:MSG:SEND,0-0-255-255,s=255,c=3,t=20,pt=0,l=0,sg=0,ft=0,st=NACK:
Jun 22 21:12:00 DEBUG New connection from 127.0.0.1
Jun 22 21:12:00 DEBUG GWT:TSA:C=0,CONNECTED
Jun 22 21:12:00 DEBUG GWT:RFC:C=0,MSG=0;0;3;0;2;
Jun 22 21:12:00 DEBUG GWT:RFC:C=0,MSG=0;0;3;0;2;Get Version
Jun 22 21:12:01 DEBUG GWT:RFC:C=0,MSG=0;0;3;0;18;PING
Jun 22 21:12:11 DEBUG GWT:RFC:C=0,MSG=0;0;3;0;18;PING
...

I tried with MySensors v. 2.3.2 and 2.4.0-alpha, same situation.

Configure command:
./configure --my-gateway=ethernet --my-port=5003 --my-transport=rfm95 --my-rfm95-irq-pin=22 --my-rfm95-cs-pin=24 --my-rfm95-rst-pin=29

(was !TSM:INIT:TSP FAIL with the grounded Reset pin, Adafruit RFM95 transceiver breakout)