[HELP] Modbus TCP “Connection refused” on ports at gateway start when using TCP slave devices

[szdavid0504]

Describe the issue I created 3 Modbus TCP slave devices in ThingsBoard Gateway. When I start the TB Gateway service, I get random “Connection refused” errors to the target host/ports. After a restart, sometimes one of them comes up, sometimes all three do — it feels non-deterministic.

What I expected to happen All three Modbus TCP slave devices should start reliably on service start, without intermittent connection failures.

What actually happens On service start I frequently see the errors above. If I restart the service, sometimes one device starts, sometimes all three, sometimes none. The behavio

Configuration (Attach your configuration file) Configuration (one of the 3 similar slave blocks): { "master": { "slaves": [] }, "slave": { "type": "tcp", "host": "192.168.0.3", "port": 5024, "method": "socket", "deviceName": "DeviceTest_API1", "deviceType": "default", "sendDataOnlyOnChange": false, "pollPeriod": 2000, "sendDataToThingsBoard": true, "byteOrder": "BIG", "wordOrder": "BIG", "unitId": 1, "values": { "holding_registers": [ { "timeseries": [ { "tag": "setLPARAM", "type": "16int", "objectsCount": 1, "address": 6151, "value": 0 }, { "tag": "setLTIME", "type": "32uint", "objectsCount": 2, "address": 4432, "value": 0 } ], "rpc": [ { "tag": "setLPARAM", "type": "16int", "functionCode": 6, "objectsCount": 1, "address": 6151, "value": 0 }, { "tag": "setLTIME", "type": "32uint", "functionCode": 16, "objectsCount": 2, "address": 4432, "value": 0 } ] } ] } },......

Connector name (If you need help with some connector/converter): Modbus TCP connector

Error traceback (If it was raised):

ERROR tcp:187 Connection to (192.168.0.3, 5024) failed: [Errno 111] Connection refused
ERROR tcp:187 Connection to (192.168.0.3, 5025) failed: [Errno 111] Connection refused
ERROR tcp:187 Connection to (192.168.0.3, 5026) failed: [Errno 111] Connection refused

**Versions:**
 - OS: Ubuntu 24.04]
 - Thingsboard IoT Gateway version 3.5.1, 3.7.0 and newest
 - Python version [e.g. 3.9]

 **Additional context**
Add configuration files, logs or any other context about the problem here.