Looks like the error related to Thermal Noise Removal is still present for products assembled using S1 Slice Assembly. Noise removal works for the individual products. Products were assembled using the same version of SNAP (SNAP v6.0.1 and S1TBX v6.0.2).
P.S. tried the individual Thermal Noise Removal operator as well as SLC>GRD graph. Fails for both. When using SLC>GRD graph:
Error: [NodeId: TOPSAR-Deburst] java.lang.NullPointerException