Many thanks for your advice. For good or bad, reality is never black or white, but shades of grey. I already thought on switching to RFM69 or try the new LoRa but that would mean switching around 15 already functioning nodes, together with the associated cost. Out of those 15, the few showing problems to communicate with the gw are the furthest ones; those are where where I'm planning to give an oportunity to the new modules linked above. By the way, my gateway already has one PA+LNA module inside, but with an external whip antenna. I actually just installed the first one. I removed the "normal" nrf24 and switched by one of these in the most problematic node. Soldering the wiring into the 1.27mm holes was a challenge; some adapters that should make connection easier should be about to arrive but I was eager to run some tests. For the moment this module seems to have less problems to connect to the gateway - of course I won't be able to draw more final conclusions until it's been in use for some days, but for the moment it looks promising. Of course, should they finally not show a significant improvemen over the former modules, I'll consider testing some of the other options.