Could it be the ants??
One possible answer:
Problem: Cucumber mosaic
Affected Area: Leaf, Stem, and Fruit
Description: Vines are stunted, new leaves are dwarfed, mottled, distorted [ours aren't] and may wilt and die. Fruit distorts and yellows early. [Ours aren't yellowing.]
Control: Plant resistant varieties. Control aphids and cucumber beetles. Rotate placement from year to year.