Dear Alessio,
Apologies for the delayed response. Unfortunately, I have not been working on the RAK3172 for some time. The last I worked on it was the middle of last year.
However, from what I can remember, flashing the RAK3172 with an older version seemed to solve the problem. See my reply to this other thread here: https://forum.rakwireless.com/t/rak3172-module-no-longer-response-after-re-uploading-hex-firmware-through-stm32cube/9092/2
Also my original Arduino IDE sketch did not use I2C or the Wire library. It only used the Serial1. Thus it seems strange that the Wire library is causing the same problem.
Will update you when I resume work on the RAK3172.
Cheers,
Ethan