Ok, I'll post a runnable code if I will be able to reproduce the error.
I posted a slimmed down version because a print() instruction makes all the difference between a completely working code and a -127 mess.
The sensor works fine, (no parasite) as the provided library examples and my program (with the print) works fine.
really, by simply toggling the comment from that print, everything works fine.
I'll try to make an mcve, when I'll actually be able to identify and isolate the problem (I understand that the print() call isn't a proper fix)