I thought I finally got it, but no. After some time the sensor and server are no longer communicating. Will try some other things to see if I can get things right.
There is program called scanner. It uses NRF24L01 to scan all channels. Run this program to see traffic on each NRF channel. Then select free channel for your NRF sensor network.
In my area channels 0-85 are pretty busy and Channels above 85 are free - I think they are not permitted to use in EU.