generation problem for HWW

Dear experts:

When generating events for p p > h, h > w+ w- > l+ vl l- vl~, using:
import model heft
generate p p > h, h > w+ w- > l+ vl l- vl~
output HWWheft
launch HWWheft
I found most events in the lhe file has only 8 particles(including only 1 W boson of mass about 80GeV), and for a small part of the events, there are 9 particles(including the 2 W bosons of mass about 60GeV).
Could you please tell me why this happens? Many thanks in advance!

Best regards

Examples of the events are like the follows:
<event>
 8 1 +2.4601970e-01 1.25001100e+02 7.54677100e-03 1.23506800e-01
       21 -1 0 0 502 501 +0.0000000000e+00 +0.0000000000e+00 +6.1894393188e+00 6.1894393188e+00 0.0000000000e+00 0.0000e+00 -1.0000e+00
       21 -1 0 0 501 502 -0.0000000000e+00 -0.0000000000e+00 -6.3112666710e+02 6.3112666710e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
       25 2 1 2 0 0 +0.0000000000e+00 -8.8817841970e-16 -6.2493722778e+02 6.3731610642e+02 1.2500112333e+02 0.0000e+00 0.0000e+00
      -24 2 3 3 0 0 +1.5317132456e+01 +6.3345449183e+00 -4.7760288074e+02 4.8463785503e+02 8.0589067707e+01 0.0000e+00 0.0000e+00
      -15 1 3 3 0 0 -1.0711560409e+01 -1.1278877638e+01 -2.1154946250e+01 2.6318056293e+01 1.7770000000e+00 0.0000e+00 1.0000e+00
       16 1 3 3 0 0 -4.6055720470e+00 +4.9443327201e+00 -1.2617940079e+02 1.2636019509e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
       15 1 4 4 0 0 +1.1645236293e+01 +2.4994731141e+01 -5.4469165705e+01 6.1076966647e+01 1.7770000000e+00 0.0000e+00 -1.0000e+00
      -16 1 4 4 0 0 +3.6718961628e+00 -1.8660186223e+01 -4.2313371503e+02 4.2356088839e+02 0.0000000000e+00 0.0000e+00 1.0000e+00
<mgrwt>
<rscale> 0 0.12500112E+03</rscale>
<asrwt>0</asrwt>
<pdfrwt beam="1"> 1 21 0.95222134E-03 0.12500112E+03</pdfrwt>
<pdfrwt beam="2"> 1 21 0.97096420E-01 0.12500112E+03</pdfrwt>
<totfact> 0.35456620E+06</totfact>
</mgrwt>
</event>
<event>
 9 1 +2.4601970e-01 1.25009000e+02 7.54677100e-03 1.23505500e-01
       21 -1 0 0 502 501 +0.0000000000e+00 +0.0000000000e+00 +1.4917658963e+01 1.4917658963e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
       21 -1 0 0 501 502 -0.0000000000e+00 -0.0000000000e+00 -2.6189160864e+02 2.6189160864e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
       25 2 1 2 0 0 +1.7763568394e-15 +0.0000000000e+00 -2.4697394968e+02 2.7680926761e+02 1.2500895493e+02 0.0000e+00 0.0000e+00
       24 2 3 3 0 0 +2.6797021934e+00 -3.1985522052e+00 -1.2220226952e+02 1.3583092344e+02 5.9154319777e+01 0.0000e+00 0.0000e+00
      -24 2 3 3 0 0 -2.6797021934e+00 +3.1985522052e+00 -1.2477168017e+02 1.4097834416e+02 6.5494349467e+01 0.0000e+00 0.0000e+00
      -11 1 4 4 0 0 -1.0079590855e+01 -2.5212984901e+01 -9.4015911334e+01 9.7858491422e+01 0.0000000000e+00 0.0000e+00 1.0000e+00
       12 1 4 4 0 0 +1.2759293048e+01 +2.2014432696e+01 -2.8186358181e+01 3.7972432020e+01 0.0000000000e+00 0.0000e+00 -1.0000e+00
       11 1 5 5 0 0 +1.6272229570e+01 -6.5450414199e+00 -1.1698166332e+02 1.1828919044e+02 0.0000000000e+00 0.0000e+00 -1.0000e+00
      -12 1 5 5 0 0 -1.8951931763e+01 +9.7435936250e+00 -7.7900168491e+00 2.2689153726e+01 0.0000000000e+00 0.0000e+00 1.0000e+00
<mgrwt>
<rscale> 0 0.12500895E+03</rscale>
<asrwt>0</asrwt>
<pdfrwt beam="1"> 1 21 0.22950245E-02 0.12500895E+03</pdfrwt>
<pdfrwt beam="2"> 1 21 0.40291015E-01 0.12500895E+03</pdfrwt>
<totfact> 0.57427273E+06</totfact>
</mgrwt>
</event>