I make vinaigrette's using dehydrated fruit powders. Been doing it the same way for over a year. Now all are fermenting and fizzing. I mix the powder with agave nectar, wisk my oil and vinegar separately, combine both with water blend and bottle. I have 10 flavors and vinegar varies from red wine, white wine,balsamic and apple cider. I recently tried the hot fill method, still fizz! I'm stumped after doing it one way so long..now I can't seem to get it right. Please advise.
The recipe you described will not produce a shelf-stable mixture. The acidity is too low to inhibit the growth of bacteria or mold, and any stray wild yeasts will greedily eat up the agave nectar.
I can't say why this is only now happening. My first guess would be that one of your ingredients previously contained an added preservative, and no longer does so. If that were the case, adding some preservative on your own could help; but preservative dosing takes you out of the realm of Official FDA Recommendations and is thus out-of-scope for this site.
In any case, there's nothing intrinsic to your recipe that would prevent microbe growth. The mystery is not why things are bad now, but why they were okay before.
Are you keeping these at room temperature? You should be fine if you keep them in the fridge. That being said, Fermentation is a result of temperature (warm ferments faster), sugar (which you're adding), cultures (which you might be adding via apple cider, wine, or fruit), water (which you have a lot of) and time. If you don't want to mess around with your ingredient ratios to make it more acidic or less sugary you can also do smaller batches so you use it before it ferments.