internal cross references in notebook for ch 17 are broken

[murphyk]

In several parts of https://github.com/fastai/fastbook/blob/master/17_foundations.ipynb, the cross references are broken.

For example, the section labeled "Broadcasting" says

As we discussed in <
Broadcasting gives specific rules to codify ...

The paperbook says

As we discused in Chapter 4, {\em broacasting} is a term...
Broadcasting gives specific rules to codify ...

A similar problem occurs in the section "The Forward and Backward Passes" and possibly elsewhere (I did not check).

[joronoso]

I have this problem not just on chapter 17, but pretty much on every chapter. Internal references don't display, and the rest of the paragraph also doesn't show.

[leonzhao101]

I also have this problem, I have tested on both colab and local jupyter, both of them have problems with cross references.