If you look on the Windstar website, and look at excursions, you will notice that there are no afternoon excursions on April 2, and the watersports platform is not open when at Motu Mahaea and the beach lunch is on a Motu. Also, there are no evening excurions on April 5 on Bora Bora, as this would conflict with the beach dinner. Also, from what I understand, the beach dinner is always on the 2nd night of the Bora Bora visit.
If you search the Windstar website for your cruise (as if you were going to purchase it), and click on itinerary and excursions, they list each island stop and there is a column indicating if the watersports platform is open.
https://www.windstarcruises.com/cruise/shore-excursions/tahiti/papeete-to-papeete/tahiti-the-tuamotu-islands/?pkgid=318754
See you soon......