Parfor freeze after ~50/70% of iteration

I'm tring to run some code that executes parfor for some data, I notice that after a lot of iteration parfor "freeze" and it's executed run like single core. I can see via top command that for some time all run correctly but after some iteration like 70/100 or something else it's freeze and the loop go slowly. The code that i'm trying to execute is the following:

for it = 1:100
  parfor ...
  % something
  end
end

Which could be cause of this freeze?

[Andrea Stevanato]

Sometimes it works correctly for all iteration.