Tcksift2 weighs fewer streamlines than expected

It’s as the title says. I have a .tck file with 200k streamlines. I’ve checked this several times over, with different toolboxes, there is 200k streamlines. However, tcksift2 produces this

This seems to indicate that there are 199825 streamlines. When I check the output .txt file, there are 200k inputs, which is good. I am confused though, is it only assigning weights to 199825 streamlines, assigning 0 weight to the rest? And if that was the case, how would it decide which streamlines are 0 weighted before the first iteration?

Thanks in advance!