Is there a common cause of low liver enzymes?

Usually OK. When we talk about liver enzymes, we are usually referring to transaminases (sgot/sgpt, ast/alt). The lower limit of normal is either zero or close to zero. Therefore having a low value of one of these is not an issue. Albumin and protein can be low in malnutrition or protein-losing kidney disease. And severe malnutrition will cause everything to be very low across the board.
See below. Deficiency of pyridoxine can result in spuriously low ALT and AST.