Yep, normal...there's two types of roots...thicker down the bottom, and thinner up the top. I usually just add medium if I can. They will happily die off and turn into organic matter and rinse/repeat. An enzyme brew like cannazym will turn any dead roots into a usable form of nutrition.
Just looks like you have healthy root growth. I had a few plants that drop roots from an inch above the medium and chase the moisture.