  The linear dynamics of closed quantum system produces well known difficulties
in the definition of quantum chaos. This leads to several issues in the
theoretical justification of the equilibration and thermalisation dynamics
observed in closed experimental systems. In the case of large harmonic baths
these issues are partially resolved due to the continuous nature of the
spectrum, which produces divergent Poincar\'e recurrence times. Within this
perspective, the phenomenon of long lived quasi-stationary states (QSS), which
is a signature characteristic of long-range interacting quantum systems,
remains unjustified. QSSs often emerge after a sudden quench of the Hamiltonian
internal parameters and present a macroscopic life-time, which increases with
the system size. In this work, the spectrum of systems with slow enough
decaying couplings is shown to remain discrete up to the thermodynamic limit,
hindering the application of several traditional results from the continuous
theory of many-body quantum systems. Accordingly, the existence of QSSs is
connected with the presence of finite recurrence times in the observables'
dynamics and with the failure of the \emph{kinematical chaos} hypothesis.
