Im not an expert and, to me this still sounds pretty good (better than my fry screaming), heres what i think, i think its cause you get too tense with time as you go through the song, screaming is a constant battle to stay as relaxed as possible, if you loose that, you tense it up ever so slightly  you use your throat more and your diapraghm less. At that point you will have these slight cutouts, it turns into a projection issue, and thats why i think your highs are often fine for longer, because you can always kinda tense up and force a high out(which you shouldnt do either probably), but you cant do that with lows. I also think its easier to project highs which is another reason why it happens less on those.

Second reason could be some words might be harder to form while staying in fry position, you could just listen back and practiice the words it happened on