Whats on the stalk of my seedlings?

Hello, my babies seem to be growing just fine, but just recently the base of the stalks started getting wierd looking markings on them. JW wtf it is cuzz I don't recall the strain getting it on my first grow, is it nutrient burn/buildup? Disease? Or are they just growing so damn fast that the stalks shred? Hopefully thats the problem , cuzz they look really healthy otherwise.
Heres some pics. Thanks for any help!

Normal stalk growth...nothing to worry about.

totally normal - sometimes it'll peel back like plastic lol

Yea this happens with healthy quick growth, also if you see little white bumps start to form around your stalk don't fret on that either, just means your plants are accepting light well and would like to grow more stems off of the bottom but doesn't have the light to do it! Doesn't mean it has to grow more either, right now I have plants with those white bumps at bottom too, while its peeling back with that plastic like substance, because of fast growth.