There have been numerous reports of mixing issues when either Roundup PowerMax 3 or Gramoxone is added to the tank with residual herbicides like atrazine, Cotoran, Caparol, fomesafen or a pyroxasulfone containing product.  What happens is the white herbicides will often clabber up and stop up screens and strainers in the sprayer.

Herbicide compatibility issues are typically caused by the pH in the tank getting too high.  As such they are hard to predict as the pH of many water sources used for spraying do not stay static.  The pH can and will change on any given day.

The easiest way to avoid this mess is to acidify the tank with AMS or one of the many AMS substitutes like Class Act, Choice, Quest, etc.  Most use one of the AMS substitutes and typically at a rate of 1% v/v.  The best approach is to add water to the tank, start the agitation and then add the AMS substitute.  Next add the white herbicides and then glyphosate or Gramoxone + surfactant.