For all 4d N = 4 SYM theories with simple gauge groups G, we show that the residues of the integrands in the N = 4 Schur indices, which are related to Gukov-Witten type surface defects in the theories, equal the vacuum characters of rank G copies of bcβγ systems that provide the free field realization of associated N = 4 VOAs in [1]. This result predicts that these residues, as module characters, are additional solutions to the flavored modular differential equations satisfied by the original Schur index. The prediction is verified in the G = SU (2) case, where an additional logarithmic solution is constructed.