  Using one of the largest volumes of the hydrodynamical cosmological
simulation suit Magneticum, we study the evolution of protoclusters identified
at redshift = 4, with properties similar to SPT2349-56. We identify 42
protoclusters in the simulation, as massive and equally rich in substructures
as observed, confirming that these structures are already virialized. The
dynamics of the internally fast rotating member galaxies within these
protoclusters resembles observations, merging rapidly to form the cores of the
BCGs of the assembling clusters. Half of the gas reservoir of these structures
is in a hot phase, with the metal-enrichment at a very early stage. These
systems show a good agreement with the observed amount of cold star-forming
gas, largely enriched to solar values. We predict that some of the member
galaxies are already quenched at z = 4, rendering them undetectable through
measurements of their gas reservoir. Tracing the evolution of protoclusters
reveals that none of the typical mass indicators at high redshift are good
tracers to predict the present-day mass of the system. We find that none of the
simulated protoclusters with properties as SPT2349-56 at z = 4.3, are among the
top ten most massive clusters at redshift z = 0, with some barely reaching
masses of M = 2 x 10^14Msun. Although the average star-formation and
mass-growth rates in the simulated galaxies match observations at high redshift
reasonably well, the simulation fails to reproduce the extremely high total
star-formation rates within observed protoclusters, indicating that the
sub-grid models are lacking the ability to reproduce higher star-formation
efficiency (or lower depletion timescales).
