Unfortunately I do not have another sensor (of the same type), nor the oscilloscope for electric measurements (sigh!).
Anyway, I will try to get the latter because I don't want to leave the question open!
However, I agree with your hypothesis, it may be a tolerance problem of the device \ sensor respect to the low-level timings applied by Espruino (if I understand well).
This leads me to ask a question (for purely cognitive purposes) about how low level operations are organized in Espruino (e.g. for the oneWire interface).
For example, how does a reset pulse is sent on the OneWire interface?
Sorry if it's a trivial question maybe, but it's just for better know some details that could explain some difference with the working implementation on the same board...
The OneWire Class and the DS18B20 sensor module correctly hide these "electrical" aspects and only expose functions to send and receive bytes, initialize the line, get the temperature value etc, etc, ...
Thanks in advance for the feedback!