@boozz I see your point, maybe I'll do this as you suggest - bit codding.
My thinking was due to way how I want to do this in Node-RED:

@mfalkvidd I didn't check this yet, but rememebr that noticed messages st=fail earlier, but I'm using power supply 2.5A, so this should be enough, but will check this once again. And go through the debug guide.

Anyway thanks guys for help.

How exactly ACK mechanism works like?

1. I'm using Serial GW, should I implement ACK confirmation in my controler or Serial GW handle this?
2. If I'm sending message from NODE1 to NODE2 through Serial GW (NODE1->SerGW->NODE2) should ACK be sent from GW to NODE1 too or NODE2 should be responsible for sending ACK to NODE1 when received?
   Generally ACK is handled in low level implementation or should I carry about it in my code?
   Thanks in advace.
   Regards

@gvorster It was some time ago but remember that finally was able to use this script: https://github.com/Yveaux/MySensors_MQTTGateway/blob/master/mqttGateway2.pl
However currently switched to this: https://www.mysensors.org/build/raspberry
and must say that works fine for me, and without extra Arduino (just RPi3 and nRF24L01+).