I take KRISTALOSE/Lactulose daily. Can this cause lactic or metabolic acidosis? Are there any recommendations for monitoring?

No, It is inert. Kristalose, a brand of lactulose, is an indigestible disaccharide for treating constipation. It arrives intact in the large bowel. Bacteria break it down to lactic and formic acid increasing osmotic pressure, drawing in water, softening stool in one to two days due to transit time to the colon. Antacids may inhibit it's effect. In the elderly, it may disrupt electrolyte balance in six months.