Check through the five reasons listed above. The reason could also be that no boards have yet been created.
In the app, all moments shared by teachers as boards are listed in chronological order with most recent at the top.
If you see 'Reset all filters' in red below, tap this first to clear any tags that are influencing what you are shown

Notice below that 'No boards match your filters' is displayed which confirms what's happening. Tap Reset all filters to see all boards again.

The view changes for other reasons and can be reset as described in each case.