Problems with figure in temporal_spectra.py file

Problem on the figure of the temporal_spectra.plot_spectra() module.
The curve seems to have undesirable Omega values.

Python 3.8.8 | packaged by conda-forge | (default, Feb 20 2021, 16:22:27) 
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In [1]: from fluidsim import load_sim_for_plot as load
   ...: sim=load()
*************************************
Program fluidsim
sim:                <class 'fluidsim_core.extend_simul.extend_simul_class.<locals>.NewSimul'>
sim.output:         <class 'fluidsim.solvers.ns3d.strat.output.Output'>
sim.oper:           <class 'fluidsim.operators.operators3d.OperatorsPseudoSpectral3D'>
sim.state:          <class 'fluidsim.solvers.ns3d.strat.state.StateNS3DStrat'>
sim.time_stepping:  <class 'fluidsim.solvers.ns3d.time_stepping.TimeSteppingPseudoSpectralNS3D'>
sim.init_fields:    <class 'fluidsim.solvers.ns3d.init_fields.InitFieldsNS3D'>
sim.forcing:        <class 'fluidsim.solvers.ns3d.forcing.ForcingNS3D'>

solver ns3d.strat, RK4 and sequential,
type fft: fluidfft.fft3d.with_pyfftw
nx =      4 ; ny =      4 ; nz =      4
Lx = 7.5 ; Ly = 2.25 ; Lz = 0.75
path_run =
/.fsnet/project/watu/2020/20MILESTONE/Bardant/milestone/ns3d.strat_300x90x30_V7.5x2.25x0.75_N0.5_Lf7_U0.1_D0.25_2021-05-12_15-18-14
init_fields.type: constant

Initialization outputs:
sim.output.phys_fields:       <class 'fluidsim.base.output.phys_fields3d.PhysFieldsBase3D'>
sim.output.spatial_means:     <class 'fluidsim.solvers.ns3d.strat.output.spatial_means.SpatialMeansNS3DStrat'>
sim.output.spatial_means_regions:<class 'fluidsim.extend_simul.spatial_means_regions_milestone.SpatialMeansRegions'>
sim.output.spatiotemporal_spectra:<class 'fluidsim.solvers.ns3d.output.spatiotemporal_spectra.SpatioTemporalSpectraNS3D'>
sim.output.spectra:           <class 'fluidsim.solvers.ns3d.strat.output.spectra.SpectraNS3DStrat'>
sim.output.spect_energy_budg: <class 'fluidsim.solvers.ns3d.strat.output.spect_energy_budget.SpectralEnergyBudgetNS3DStrat'>
sim.output.temporal_spectra:  <class 'fluidsim.base.output.temporal_spectra.TemporalSpectra3D'>

Memory usage at the end of init. (equiv. seq.): 177.41796875 Mo
Size of state_spect (equiv. seq.): 0.003072 Mo

In [2]: sim.output.temporal_spectra.plot_spectra(key='vx',tmin=150)
load times series...
Getting times from rank 0... ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 0:00:00
tmin= 150.832, tmax= 299.538, nit=72
Rearranging... ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 0:00:00
Rank 00009...  ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100% 0:00:00