  We present results of simulations of light-nuclei production in Au+Au
collisions at collision energy of $\sqrt{s_{NN}}=$ 3 GeV within updated
Three-fluid Hydrodynamics-based Event Simulator Extended by UrQMD
(Ultra-relativistic Quantum Molecular Dynamics) final State interactions
(THESEUS). The results are compared with recent STAR data. 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.
It is found that the late freeze-out is preferable for deuterons, tritons, and
$^3$He. Remarkably, the $^4$He observables are better reproduced with the
standard freeze-out. This suggests that the $^4$He nuclei better survive in the
afterburner stage because they are more spatially compact and tightly bound
objects. This is an argument in favor of dynamical treatment of light nuclei.
The simulations indicate that the collision dynamics is determined by the
hadronic phase. The calculated results reveal not perfect but a good
reproduction of the data on bulk observables and directed flow. The elliptic
flow turns out to be more intricate.
