Ran into the same error. I think it’s got to do with the move to the rewritten
What fixed it for me was just reverting to an earlier, working commit by issuing:
git checkout 2e1ccb58121dc648751e2109fc0fbf6925aa8887
That puts the repo back to an earlier stage which gets everything working for me again. Note that this isn’t a resilient fix: if you intend to work on the fastai library code, this definitely wouldn’t be the way to go. Then again, if that’s the case, you probably know enough to fix the underlying root cause.