concurrent testing of login functionality with 50 users/threads is not working

i have given the thread count = 50 rampup period =0

for 48 threaads it is getting passed , for 2 threads there is no failure captured in the selenium log files.

I am expecting concurrent login of 50 users with 0 rampup period , i am not able to find out the exact reason of failure . please suggest the fixes to handle this scenario.