Yesterday I tested the range of nRF24L01+ modules used in the device and I was not happy. It was simply not working as reliable as it must so I made a little change.
I had to switch to the version with PA+LNA (which I luckily had at hand). These work much better and hopefuly it will not drain the battery too much during RX/TX.
It had to be connected with wires because this version is much "longer" and there is simply no space in the current enclosure.