Q.Losing plant fast
I purchased vinyl raised bed kits this year for the first time. I always planted directly in the ground and never had any trouble. My zucchini started to get yellow and then brown and got crunchy on the ends. It seamed to start at one end and work its way down to the other end. I also have spots on my pepper and green bean plants. Everything was beautiful for the first 3 weeks or so, then BAM!
I would start with checking the watering and moisture levels in your soil.
Raised beds soil will dry out much faster and you will need to water more often.
Also if water is splashing unto the leaves of your plants it can cause fungus diseases.
Check the plants for pests. If the issue is moving through the garden, it could certainly be caused by an infestation. Some insects are very difficult to see.
Here are some links that will help you.