Q.Gardenia plants
What causes a perfectly healthy indoor plant that is full of buds to suddenly have the buds flop over and fall off?

Certified GKH Gardening Expert
It sounds like you have thrips. This article will help with that:
https://www.gardeningknowhow.com/plant-problems/pests/insects/controlling-thrips.htm
I would recommend using neem oil to treat them. We have found it to be effective against pests like this. Here is more information on that:
https://www.gardeningknowhow.com/plant-problems/pests/pesticides/neem-oil-uses.htm
This article may also help: https://www.gardeningknowhow.com/ornamental/flowers/gardenia/gardenia-flowers-gardenia-buds-falling-off-plant.htm