Bottom leafs fallen off?

Hello I was looking at my cannabis plants this morning they are about 1 week into flowering and I noticed that the very bottom leafs (2) have fallen off not the typical cannabis looking leads but the normal looking leafs you get after the shell falls off also some of the other plants have the bottom leafs turning yellow

Could be poor light penetration ....if thats the case this is normal the plant is killing lower growth so it can use its energy on the tops and since your flowering that is where your new growth has been...If this seems to be the problem just add some more wattage or if you have a nice canopy just do a good prune! its early flower they will recover

in order for the bud sites to grow they use the energy from those fan leaves to grow so once a bud site branch is about to start growing they start fallin off at the bottom because there isnt enough sufficient light gettin to that part of the plant .....

Those first set of leaves always fall off...