The separate Lessons page has been retired. Your lessons live in My Library alongside your pathways and tutors.
Where to look
Click My Library in the sidebar, then set the type filter to Lessons. The Lessons link under My Library does the same in one click.
What you get instead
Folders, so you can group by term, grade or topic.
Search and filters by type and by when something was made.
Shared with me for items colleagues sent you, and Trash for anything deleted.
Nothing was lost in the move.