The matter for effect is how many or percent occurence of the sap ball on the field in general. If they are very few as compared to the field, it won't affect yield
Guttation/ It is common on young plants, especially some varieties, with sufficient water level in in soil.
According to the Ontario (Canada) Ministry of Agriculture "Tender Fruit Grape Vine Newsletter for Commercial Fruit Growers" (Volume 11, Issue 5 May/June 2007) these are sap droplets called grape pearls or sap balls.
"Grape pearls are small sap-like, fluid-filled balls that are exuded from surface cells of rapidly growing grape vines. They appear most commonly in the spring and are often confused with mite or insect eggs. Some vines have many grape pearls but the pearls can appear singly or in smaller groups. They are usually found on the underside of leaves but can be on shoots as well. Grape pearls, also called "sap balls" are of no consequence to the vine." https://hortnews.extension.iastate.edu/2009/6-3/grapepearls.html