@Ashok,
Thank you very much, that was the trick needed. After triggering the reed switch multiple times (no idea when I should do it specifically) while the sensor was in the "Getting sensor info..." stage, all of them paired and are working without any trouble at all.
Another plus with these sensors that I was not sure about (some sites mentioned it but some did not nor did their manual), but is now proven, is that they provide the temperature as well. All of them are accurately reporting the temperate in the app, LCD, webpage, and in Rules as well. Excellent!