  In the RHIC Beam Energy Scan program, gold nuclei are collided with different
collision energies in the range from few to 62.4 GeV. The goals of the program
are to explore the onset of QGP creation, locate the critical point of QCD and
study dense baryon matter. We report on the first application of Monte Carlo
Glauber (GLISSANDO2) and T$_{\rm R}$ENTo $p=0$ initial states extended to 3D
for event-by-event viscous fluid dynamic (vHLLE) with hadronic cascade
modelling of Au+Au collisions at $\sqrt{s_{_{\rm NN}}}=27$ and 62.4 GeV, which
is the upper region of RHIC BES energies. The initial states are extended into
both the longitudinal direction and for finite baryon density using simple
ans\"atze. The full energy and baryon charge counting in the initial states is
implemented. We show the reproduction of elliptic flow, at both collision
energies and with both initial states. We compare it also to the results
obtained with UrQMD initial state. Furthermore, we show the results for
rapidity decorrelation of elliptic flow $r_2$ at $\sqrt{s_{_{\rm NN}}}=27$ and
200 GeV from the same setup of hydrodynamic calculations with the 3D Monte
Carlo Glauber and UrQMD initial states. We discuss the features of the initial
states responsible for the magnitude of the observed flow decorrelation.
