  We present results of simulations of light-nuclei production in relativistic
heavy-ion collisions within updated Three-fluid Hydrodynamics-based Event
Simulator Extended by UrQMD (Ultra-relativistic Quantum Molecular Dynamics)
final State interactions (THESEUS). The simulations were performed for Pb+Pb
and Au+Au collisions in the collision energy range of $\sqrt{s_{NN}}=$
6.4--19.6 GeV. The light-nuclei production is treated within the
thermodynamical approach on equal basis with hadrons. The only additional
parameter related to the light nuclei is the energy density of late freeze-out
that imitates afterburner stage of the collision because the light nuclei do
not participate in the UrQMD evolution. This parameter is fixed from the
condition of the best reproduction of the proton transverse-momentum spectrum
after the UrQMD afterburner by that at the late freeze-out. The updated THESEUS
results in not perfect, but a reasonable reproduction of data on bulk
observables of the light nuclei, especially their functional dependence on the
collision energy and light-nucleus mass. Various ratios, $d/p$, $t/p$, $t/d$,
and $N(t)\times N(p)/N^2(d)$, are also considered. The directed flow of light
nuclei turns out to be more involved. Apparently, it requires explicit
treatment of the afterburner evolution of light nuclei that violates the
kinetic equilibrium. Imperfect reproduction of the light-nuclei data leaves
room for medium effects in produced light nuclei.
