It is possible that you may have, without intending to, moved or removed that unit or chapter.
Search units and chapters for missing chapter
Before you contact tech support, simply look through the units/chapters before and after the missing chapter to see if it was accidentally moved. If it was, you can drag it back to the right spot.
In the example below you can see that Chapter 9 was accidentally dragged inside Chapter 10.
Check "Removed Content" area
You may have removed an entire unit when you intended to remove just one resource in the unit/chapter. To check the Removed Content area follow the instructions below.
Note: While you can add individual items back into your course if you remove them, you cannot currently re-add a unit if you remove it. If you have removed a unit and wish to restore it, please contact tech support.
Click "+ Add" to restore the removed contentHover over the item you want to add and a + Add link will appear to the left of the item. Click it to restore the item.
The item will return to the location where it last lived so you may have to click and drag it elsewhere if you want it to live in another unit/chapter.
If you still can’t locate the item, please contact tech support.