dsurendr
Ansys Employee

In reference to this thread: 

https://studentcommunity.ansys.com/thread/domain-decomposition-in-hfss/

asamaiyar - Whenever you're running a hybrid solution (combination of FEM and MOM in your case), the domain solver will be used. To use Direct solver only, you must use only one solver time (all FEM for example --- in your case, change FEBI boundary to Radiation or PML).