Thanks Steve! After I reduced the mesh size, the ADI mode solver returned one mode. However, the mode is a bit different from the mode found by the FD method.
Modes Modal Index Polarization
Mode 1 2.31022444, -0.00336495 FVect TE (by ADI method)
Mode 1 2.34768099, 0.0 FVect TE (by FD method)
The project is attached. Thanks for your help!