Hi Dave,
I think the issue comes when the macros are used with generate loop.
The complete code is :
define WB_DUT_U_ASSIGN(phy_i,idx)\ assign b[phy_i] = DUT_PATH.Ilaneidx.a;\
genvar wb
generate
for(wb=0;wb<8;wb++) begin:wb_a
`WB_DUT_U_ASSIGN(wb,wb)
end
endgenerate