Hi sretodd,
In that style of bowed slat system, if it is assembled properly and all of the plastic inserts are properly pressed into their corresponding holes and the bowed slats are all appropriately inserted into their plastic holders, then a slat falling through would be an indication of a defect in the bowed slats (having lost their resilience or cut too short) or breaks in the plastic sleeves holding these slats.
The easiest fix for this would be to remove the slats and corresponding plastic holders and place a solid deck on top of this frame network, and then place a coir bed rug or similar on top of this deck for air circulation. And I would address this regardless of the style/type of mattress you choose.
While it’s not possible to “diagnose” mattress comfort issues on a forum with any certainty because they can be very complex and there are too many unique unknowns, variables, and complexities involved that can affect how each person sleeps on a mattress in terms of “comfort”, firmness, and PPP or any “symptoms” they experience … there is more about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here.
Upper back and neck pain are most often associated with your pillow. Make sure whatever you’re using helps you maintain a neutral alignment. And as you’ve only had the mattress for a few days, this is much too short of a time to make a judgement on this mattress, and you’ve not had enough time to adjust to this new product, nor had the mattress had enough time to “adjust” to you. I would wait at least a few weeks before making any decision, at which time if you’re still having issues I would place a phone call to Sleep on Latex and seek their advice, as they will be best suited to provide useful suggestions that they feel might work best for your situation.
Phoenix