@Reza I implemented your sketch, tried to start/stop(up to a few hours) the gateway(serial gateway) and the controller(domoticz on orangepi pc) to see if the logs help in some way. Nothing, it works.
It should be logged until the freeze occurs.

@Reza
there are two problems with MQ-2 sensors :
1 the sketch, at the bottom, uses log instead of log10
2 are you sure that RL_VALUE is 5 (kOhm) in your MQ-2 board? In my is 1, the one labeled 102 in the pic.

Regards

1 look at the last line of the sketch:

  return (pow(10, ( ((log(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}``

change to:

  return (pow(10, ( ((log10(rs_ro_ratio) - pcurve[1]) / pcurve[2]) + pcurve[0])));
}``

2 RL_VALUE in your MQ2 board should be 1 (kohm), R2 in the schematic.

yes, R2 is 1k. Change RL_VALUE from 5 to 1.

I suggest you use the MQ-2 sensor library https://github.com/xerlay11/MQ-2-sensor-library and obviously change log and RL_VALUE.
Regards

Which MySensors library are you using?
With 2.0 i had the sleep issue solved (for now) with MY_PARENT_NODE_ID and MY_PARENT_NODE_IS_STATIC(as suggested by tekka).

@AWI Thanks for the hint.
I thought this wasn't a "issue" but just a "really annoying thing".
However i run domoticz on a Orange PI PC with WiringOP support and i can't find precompiled images.

It should be enough to read ppm from the sensor.