The Motoko base library documentation is automatically generated from the source but incorporated into the SDK website so that it is part of the Search index. Previously, the navigation for this section was manually hand-coded, though, which meant it could easily get out of sync as new modules are added or consolidated.
In updating the site to provide more modular navigation, we removed the manually generated navigation.
The good news is that we now have the list of modules for navigation automatically generated, so I can add it back into the main left navigation bar.
The switch to the auto-generated navigation is now live.
Thanks for your patience (and kudos for noticing for quickly!) as we iterate to improve the doc available and your overall dev experience.
Feel free to reach out with comments and suggestions any time!