[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.