Hi,
Are you using Edit Guides on top or below HairFromGuides? If you are using it on top of HairFromGuides this is the expected behavior, unless you show 100% on the viewport. For example: If you use Edit Guides to groom 50% of hairs, Arnold will render 100%, the remaining 50% which is not affected by the Edit Guides in the viewport will appear unchanged in the render. If this is the case, you have to either use Edit Guides below HairFromGuides or increase the amount of hair in the viewport to 100%.
Jeordanis Figuereo (Product Designer. EPHERE Inc.)