Having trouble transitioning into my sprint stride from blocks.

It sounds like you’re pushing too much. Did it feel kind like falling over forwards? Did you feel it in the quads after that race?

Like I said this never happens to me in the 200/400, probably because of that lacking sense of urgency you get in the 100.

You answered your own question. Be patient. Essentially you’re getting over-excited and rushing things which turns into pushing. “Let the race come to you”.