Aloha Koale!
If you have had previous garden experience somewhere else, a new garden in a new setting can feel like you are suddenly a bit of a newbie again. If all of the plants are suddenly dieing and you feel they have had adequate water and fertilizer the most likely explanations would be something is wrong with the soil or the plants have contracted a disease/pest.
Out of curiosity I did a little looking up on your soil, figuring that it is most likely volcanic, and maybe that is where you have a problem. After checking out the following link
Soil Management I suspect maybe a high acid content and not enough organic material may have something to do with the problem. Since it appears that there are many different soil types and combinations on the island the exact makeup is a guess. If the gardens where plants are doing well are close by you may want to find out from the owner what was done to the soil in that garden to make it more plant friendly. The fix could be as simple as organic material (especially compost) and lime. If you can't talk to them look up the cooperative extension service for the island or the Master Gardeners for Maui. They can help you get a soil test done and what you will need to do to follow the recommendations from the lab.
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