tWZ production gets stuck while setting up grids

Dear all,

I'm trying to run tWZ production with MG5 2.9.9 or 3.3.1. Please find the proc_card below.
The production gets stuck after "setting up grids" and never progresses beyond that step even if I ask for 100 events and require accuracy -1. I have waited up to three days.

Help or advice would be very appreciated.

12:53:40 INFO: Poles successfully cancel for 20 points over 20 (tolerance=1.0e-05)
12:53:40 INFO: Starting run
12:53:40 INFO: Using 8 cores
12:53:40 INFO: Cleaning previous results
12:53:40 INFO: Generating events without running the shower.
12:53:41 INFO: Setting up grids
12:53:42 INFO: Idle: 24, Running: 8, Completed: 0 [ current time: 12h53 ]

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set group_subprocesses Auto
set ignore_six_quark_processes False
set low_mem_multicore_nlo_generation False
set complex_mass_scheme False
set include_lepton_initiated_processes False
set gauge unitary
set loop_optimized_output True
set loop_color_flows False
set max_npoint_for_channel 0
set default_unset_couplings 99
set max_t_for_channel 99
set zerowidth_tchannel True
set nlo_mixed_expansion True
import model loop_sm-no_b_mass
define p = g u c d s u~ c~ d~ s~
define j = g u c d s u~ c~ d~ s~
define l+ = e+ mu+
define l- = e- mu-
define vl = ve vm vt
define vl~ = ve~ vm~ vt~
define p = 21 2 4 1 3 -2 -4 -1 -3 5 -5 # pass to 5 flavors
define j = p
define p = g u c d s b u~ c~ d~ s~ b~
define j = g u c d s b u~ c~ d~ s~ b~
define w = w+ w-
define ttbar = t t~
generate p p > ttbar w Z [QCD]
output -f -nojpeg