problem using small width for the decaying particle (Heavy neutral lepton)

Hi

I am using this script to generate a sample for HNL with 100 mm decay length (long lived)

import model SM_HeavyN_NLO
define ee = e+ e-
define mm = mu+ mu-
define ll = e+ e- mu+ mu-
define vv = ve ve~ vm vm~ vt vt~
generate p p > n1 > mu- mu- mu+ vm [QCD]
output ATLAS_HeavyN_Major_1SFH_LNVtest1 -nojpeg
launch ATLAS_HeavyN_Major_1SFH_LNVtest1
order=nlo
shower=py8
madspin=off
set VeN1 0
set VmuN1 1
set VtaN1 0
set mN1 10
set mN2 1e12
set mN3 1e12
set wn1 197.4635212e-13 #(100 mm)
set LHC 13
set pdlabel lhapdf
set lhaid 260000
set reweight_scale true
set reweight_PDF true
set dynamical_scale_choice 3
set nevents 4000
set no_parton_cut
set jetradius 0.4
done

but the code runs for ever and stuck in this part:
INFO: Poles successfully cancel for 20 points over 20
(tolerance=1.0e-05)
INFO: P0_uxd_n1_vmmummummup
INFO: Result for test_ME:
INFO: Passed.
INFO: Result for test_MC:
INFO: Passed.
INFO: Result for check_poles:
INFO: Poles successfully cancel for 20 points over 20
(tolerance=1.0e-05)
INFO: Starting run
INFO: Using 10 cores
INFO: Cleaning previous results
INFO: Generating events without running the shower.
INFO: Setting up grids
INFO: Idle: 0, Running: 4, Completed: 0 [ current time: 10h08 ]
INFO: Idle: 0, Running: 3, Completed: 1 [ 12.4s ]
INFO: Idle: 0, Running: 2, Completed: 2 [ 12.8s ]
INFO: Idle: 0, Running: 1, Completed: 3 [ 19.1s ]
INFO: Idle: 0, Running: 0, Completed: 4 [ 19.2s ]
sum of cpu time of last step: 0 second
INFO: Determining the number of unweighted events per channel
     Intermediate results:
     Random seed: 33
     Total cross section: 5.210e+05 +- 5.2e+03 pb
     Total abs(cross section): 6.130e+05 +- 5.3e+03 pb
INFO: Computing upper envelope
INFO: Idle: 0, Running: 4, Completed: 0 [ current time: 10h09 ]
INFO: Idle: 0, Running: 3, Completed: 1 [ 22.8s ]

So I just changed the value of width to see if it works, for
wn1 =197.4635212e-10
There is no problem any more.
when I use mad spin for n1 decay, also I don't have any problem,
I was wondering for the case of NLO and small width can Madgraph handle the spin correlation effects properly? or we should use madspin?

many thanks