Your own Sentinel ult counters yourself as well

While playing cryo and preparing for the spawn rush with narrow path you can't flank and you , I managed to Crack all three shields with my lmg then they didn't try to heal but started to spawn there grenades so I deployed my ult stopped all there spam, they started to rush me with knives and shotguns, so I had 5 heat I throw them in the narrow path only one went off the others didn't even my Flechette didn't deploy it just rolled on the ground