That guide is already 2 years old; I'm not sure if it is correct. This is the official guide.
That guide is the only complete tutorial I've found to getting MySensors 2.4 working with OpenHab 2.4 via the serial gateway. While the original post is 2 years old, it has been updated multiple times. I've followed the official guide as well, to the same result, however.
Still, they can be counterfeit nRF24L01+ (e.g. https://forum.mysensors.org/topic/1664/which-are-the-best-nrf24l01-modules)
Looking at my ICs through a magnifying lens, it appears that mine have the "hole" in the middle of the "+" symbol on the etching. They were purchased from Amazon, but I can't recall which supplier.
Would you be able to build an Arduino serial gateway (e.g. based on Uno or Nano) and test if that gets the communication running?
Yeah, I can throw one together.