First you could increase incubation time and increase temperature to 37°C. One explanation for incomplete deglycosylation with IgGZERO Immobilized could be that the antibody has higher amounts of high mannose, hybrid glycans or bisected glycans. For these glycans IgGZERO has low or no activity. High mannose glycans are particularly resistant to digestion recommend you try our other endoglycosidase GlycINATOR (EndoS2). This enzyme has much higher activity on these types of glycans sometimes seen in mAbs.