Hi @miwojc,
Theres a thread and some YT videos by @slawekbiel on debugging fastai2 code
using the Jupyterlab debugger in this link
I myself tried but couldn’t step through the source but maybe that was because I didn’t use the development install for the fastai2 library.
I know @slawekbiel had a problem with training the model because using the debugger requires a different jupyter kernel (xeus-python) from the one we usually use (ipykernel) but he could set breakpoints in fastai2 and step through it.
HTH.
Butch